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The word "nominal" has a number of definitions.

For example, the Free Dictionary gives seven:

nom·i·nal (nm-nl) adj.

  1. a. Of, resembling, relating to, or consisting of a name or names. b. Assigned to or bearing a person's name: nominal shares.
  2. Existing in name only.
  3. Philosophy Of or relating to nominalism.
  4. Insignificantly small; trifling: a nominal sum.
  5. Business a. Of, relating to, or being the amount or face value of a sum of money or a stock certificate, for example, and not the purchasing power or market value. b. Of, relating to, or being the rate of interest or return without adjustment for compounding or inflation.
  6. Grammar Of or relating to a noun or word group that functions as a noun.
  7. Aerospace & Engineering According to plan or design: a nominal flight check. [...]

[Middle English nominalle, of nouns, from Latin nōminālis, of names, from nōmen, nōmin-, name; see nō̆men- in Indo-European roots.]

This consistent with the definitions in OED3 and other sources.

Most of the definitions are clearly from the sense of "names" and "nouns" - and from that idea of something being only in name, but not in reality.

However, the aerospace sense seems quite different. During a recent rocket launch, the announcer repeated phrases like "Height is nominal. Power is nominal." to mean these values were within the acceptable and expected ranges.

The OED references these sources [Hat tip @tchrist]:

6. (See quot. 1970.)

  • 1966 Aviation Week & Space Technology 5 Dec. 30/1
    The mission is to launch the 800-lb. Prime vehicle to effect a nominal re-entry at 400,000 ft. following injection at 26,000 fps.

  • 1970 N. Armstrong et al. First on Moon vi. 124
    An example of misuse is our use of the word ‘nominal’, which most of the English-speaking world interprets as meaning small, minimal-and we usually use it in the sense of being average or normal.

  • 1970 R. Turnill Lang. Space 94
    Nominal, a favourite word, meaning within prescribed limits; anything from ‘perfect’ to acceptable.

  • 1972 Daily Colonist (Victoria, B.C.) 26 July 3/1
    As one engineer said, ‘She is phenomenally nominal’ — nominal being space jargon for operating-as-planned.

I wonder if anyone can explain that derivation. Is it derived from the other senses of nominal? Is it influenced by the word "normal"?

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Wouldn't it come from definition 4? The differences from expected values are insignificantly small. –  Martin Smith Jul 13 at 17:52
    
Seems quite a jump. Imagine if the announcer said "Power is insignificantly small." (Which doesn't mean your answer is wrong, but I would appreciate evidence.) –  Oddthinking Jul 13 at 17:56
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It was a supposition not an answer. Hence not posting it as such. –  Martin Smith Jul 13 at 17:58
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It is very likely (but not certainly, thus this being a comment rather than an an answer) and extension of its use in describing parts and so forth. A nominal "6 volt" battery will only provide exactly 6V under certain specific load, temperature and age conditions, a nominal "2 by 4" is 1½ by 3½ inches (more or less) and may never have been 2 by 4 even before dressing, and so on. –  bye Jul 13 at 18:17
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I think the 1970 entry sums it up quite well - someone in a space programme made up a new usage for the word nominal. –  Frank Jul 13 at 18:18

3 Answers 3

I'm not allowed to comment yet, so I'll take a stab at answering.

I would say it derives from definition 4. In the aerospace industry, to say that something is "nominal" is to say it is within accepted parameters. Everything in the aerospace industry has accepted parameters or "tolerances".

Example: "We will accept a tolerance of this measurement between a and b." Is the same as "This measurement is between a and b, so it is nominal." Which then becomes "This measurement is nominal", where the tolerance equaling between a and b, becomes unstated, yet accepted.

By stating that something is nominal you relay the parameters it meets without having to pronounce all those numbers. And pronouncing many numbers can get confusing.

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The question here is: "How and when did definition #4 arise?" –  bye Jul 13 at 19:03
    
OK. Second try. I certainly don't mind corrections. –  distantsmoke Jul 13 at 19:56
    
One of the definitions of "nominal" according to Wikipedia:en.wiktionary.org/wiki/nominal is "normal. "Normal" is derived from the Latin "normalis" (with a bar over the a). According to the online eytomology dictionary etymonline.com/index.php?term=normal –  distantsmoke Jul 13 at 19:59
    
According to the online eytomology dictionary etymonline.com/index.php?term=normal normal (adj.) "typical, common;" 1640s, "standing at a right angle," from Late Latin normalis "in conformity with rule, normal," from Latin normalis "made according to a carpenter's square," from norma "rule, pattern," literally "carpenter's square" (see norm). –  distantsmoke Jul 13 at 20:09
    
Nice answer. It's a shortening of "The difference between this and expected are nominal" to "This is nominal" –  Mitch Jul 13 at 20:36

Someone else will hopefully provide some historical evidence. I don't have that to offer.

For my thinking, this connotation comes from the distinction between (a) what something is in name, that is, as set forth in a definition or specification and (b) what a given occurrence of that something is in concrete reality.

The "2-by-4" and other examples cited so far fit this. It especially makes sense for contexts, such as standards, where a name or symbol is invented or formally ascribed to a definition that the standards body formulates.

Such a definition sets forth what something is in name, or nominally. For a given occurrence to fit that name the definition must be matched in some way, often within tolerances specified in the definition.

If it fits then it can be called by that name - it is nominally such a thing. This is the case even if according to some other considerations one might normally not think of it as being such a thing.

It may help to think of the expression at least in name or even in name only.

Those Republicans on the far right of the American political spectrum sometimes criticize centrist Republicans as being "RINO"s (rhinos): R epublican I n N ame O nly. From their point of view the centrists are only nominally Republican, that is, according the definition of being enrolled in the party. They do not consider them to be really Republican, that is, Republican in spirit or actual practice.

The point is this: Use of the word nominally in such contexts emphasizes the possibility or actuality of a discrepancy between (a) the meaning of the name as formally or defined or as normally/conventionally understood and (b) the meaning of some individuals or occurrences that are classified under that name.

Some things called a given name do not, in some sense, seem to really correspond to what one thinks of as what that name means. There is some difference -- in some sense the name does not really seem to fit.

(This difference is close to what is meant by the letter of the law versus the spirit of the law. The former is the nominal meaning of the law.)

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This answer doesn't make sense or provide any evidence. "In name only" means that it doesn't match what it's supposed to be. "Nominal" in aerospace means that it does match what it's supposed to be, which is the opposite meaning. –  Ben Crowell Jul 13 at 21:06
    
@Ben: Please reread what I wrote. If a standards body defines round as within certain tolerances, and if something that might normally be considered round is not round according to that definition, that thing is nominally round (according to that definition). Aerospace, science, the military etc. often use formal/artificial/conventional definitions. And the vocabulary sometimes uses nominal to point out that that is what is meant. If the potential difference in meaning is disregarded/unimportant then there is no need to add nominal to the phrase. (But adding it can become habitual.) –  Drew Jul 13 at 21:24

Looking at definitions from other sources it appears that the meaning of 'nominal' in the aerospace context is close to 'normal' in the sense of within the expected range of performance. The meaning is derived from the definition n.4 given above.

Nominal :

The use of nominal in aerospace has nothing to do with names, nouns, or interest rates. It does, however, have to do with small or trivial deviations from a planned performance.

The use of nominal in aerospace generally means that a test, rocket launch, satellite deployment, etc. is going within previously determined limits and can still be expected to come to an acceptable outcome. If all continues as it has been going, the test will demonstrate that the item under test will work as expected; the rocket will achieve the proper orbit; the satellite's solar arrays, antennae, etc. will open. The rocket is where it is supposed to be and going as fast a it should this long after launch, the thrust is correct, and success is expected.

When the announcer of a rocket launch says that everything is nominal, she really means that the flight is going normally, or as expected, so far. The announcer remains calm throughout the flight, even if it ends with an explosion, perhaps calling an obvious disaster an anomaly.

Source:http://www.thelen-aerospace.com

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This is just restating what the OP already knew. The OP is asking how this meaning arose. –  Ben Crowell Jul 13 at 21:04
    
@Ben Crowell - OP is asking if 'nominal' is influenced ( somehow derived from) 'normal' (see the last sentence in the question). My take is that the use of nominal in aerospace is derived from an already existing meaning of it ( n.4 in the list) applied to the aerospace jargon as shown in the extract provided!!! –  Josh61 Jul 13 at 21:14

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