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"plumb" as far as I know is a predominantly American usage, as in "That was just plumb crazy!"

I thought plumb meant some kind of weight in bricklaying or such like, so how did it come to mean "absolutely"? What was its origin and history?

Edit: After Callithumpian's answer, I have a little addition:

Why is it a US usage chiefly, and why do not the British use it as much?

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In my experience, Brits do in fact use plumb to mean "spot-on". Eg, "that's plumb-perfect". A company comes to mind that is called "plumb-something" (meaning perfect whatever-they-sell). HOWEVER perhaps the expression "plumb crazy" is NOT used in UK (I'm not sure), and THAT is why you say "less used in the UK". ie "plumb crazy" is (perhaps) not used in the UK, but "plumb" meaning spot-on, is indeed used. BTW a funny one in the UK (particularly amongst builders) is "tits", again meaning "spot on." (So, you finish installing a window .. you exclaim, "Tits." (!)) – Joe Blow Jun 15 '11 at 15:54
up vote 4 down vote accepted

Etymonline indicates that the "completely" sense of the word was an extension of the "exact measurement" sense of the word and dates this shift back to the mid-18th:

plumb (n.) c.1300, "lead hung on a string to show the vertical line," from O.Fr. *plombe, plomme "sounding lead," from L.L. *plumba, originally pl. of L. plumbum "lead," the metal, of unknown origin, related to Gk. molybdos "lead" (dial. bolimos), probably from an extinct Mediterranean language, perhaps Iberian. The verb is first recorded late 14c., with sense "to immerse;" meaning "take soundings with a plumb" is first recorded 1560s; figurative sense of "to get to the bottom of" is from 1590s. Plumb-bob is from 1835. Adj. sense of "perpendicular, vertical" is from mid-15c.; the notion of "exact measurement" led to extended sense of "completely, downright" (1748), sometimes spelled plump or plunk.

Edit re: British vs. American use:

I found this newsletter on British plumb bobs and noticed that another word used for the tool in several publications was plummet rather than plumb-bob. Perhaps plummet was a common enough name for the tool in England that it prevented the development of the extended sense of plumb as occurred in the U.S. This is only a guess.

Edit re: confusion with plum:

After seeing the OED references in @Simon's answer, I agree with @Peter's comment that there seems to be some confusion between the etymology of plumb and plum as intensifiers. I found this on plum at Etymonline:

plum O.E. plume, early Gmc. borrowing (cf. M.Du. prume, O.H.G. phruma, Ger. Pflaume) from V.L. *pruna, from L. prunum "plum," from Gk. prounon, later form of proumnon, from an Asiatic language. Change of pr- to pl- is unique to Gmc. Meaning "something desirable" is first recorded 1780, probably in ref. to the sugar-rich bits of a plum pudding, etc.

Some of the OED references seem to be examples of plum being used to mean "something desirable" rather than misspellings of plumb meaning "completely."

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Why don't the British use it as much as the Americans? In fact, as far as I know, they don't seem to use it at all! Is there a reason why? – Thursagen Jun 15 '11 at 11:39
@Ham: See my edit as to a guess. – Callithumpian Jun 15 '11 at 11:52
@Callithumpian, a pretty good guess... – Thursagen Jun 15 '11 at 11:56
"Plumb crazy" is used in en-gb, although to my surprise BNC only has one instance. – Peter Taylor Jun 15 '11 at 12:32
I thought a plummet was a lead stylus, i.e. a writing tool? – Marthaª Jun 15 '11 at 13:58

Lots of background and examples in other answers, but I really don't see anything at all unusual in this type of 'specialised meaning'.

Plumb weights are made of lead (Pb=plumbum), and they give straight vertical lines. That explanation is straight up (absolutely true), and it's straight to the point (absolutely focussed).

Does anyone ever wonder why we use straight in such figurative senses? I can't see why the American use of plumb is much different.

Brits don't say it simply because it calls to mind American 'hicks from the sticks' who are invariably plumb loco.

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Callithumpian's answer is all you would need; except for an actual answer to 'how did it come to mean...?' Surely 'plumb vertical' is a builder's term, meaning 'precisely vertical as measured by plumbline', and it was taken up by outsiders who assumed it just meant very (I have seen it as plum as well as the variations in the dictionary).

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I would have guessed plumb straight rather than plumb vertical, but I can't find either of these expressions in Google books before 1862 (when we get plumb straight meaning exactly vertical), long after plumb was being used as an intensifier. – Peter Shor Jun 15 '11 at 14:09
@Peter Shor: My pa is a builder, and he just says a wall is plumb when it's vertical. I think anyone who says it's plumb vertical either likes tautology or likes American slang (and doesn't know the standard meaning of the word). – FumbleFingers Jun 16 '11 at 2:28
@Peter: "Plumb vertical" makes sense to me: A line can't be literally "plumb horizontal". A plumb line can only measure vertical lines. Well, I suppose in some cases you could stand the thing on end, use a plumb line to make sure it's straight, and then lie it down. – Jay Jan 19 '12 at 15:49

I find the 'plumb' arguments abstruse, myself.

If things can be 'peachy keen' why can't they be 'plum crazy'?

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Certainly there's been much conflation of plumb and plum over the centuries. – Hot Licks Jan 9 at 22:37

The history of the US slang meaning of the word goes back a bit further than the Etymonline explanation. From the OED:


c.B.2.c As an intensive: Completely, entirely, absolutely, quite. Chiefly U.S. slang.

   1587 Misfortunes of Arthur (1828) ii. iv. Chorus 41 Then rowles and reeles and falles at length plum ripe.    1787 Grose Provinc. Gloss., Plum pleasant, very pleasant.    1846 S. F. Smith Theatr. Apprenticeship 213 Long before the time arrived‥the house was plum, chock full—full to overflowing.    a 1861 T. Winthrop John Brent xxviii. 296 When we got here, I paid their tickets plum through to York out of my own belt.    1882 Burdett Life Penn v. 83 Penn‥wrote his wife and children a long letter‥which filled them plumbfull of good advice.    1893 Harper's Weekly Christmas 1211/1 ‘You're plumb crazy’, she remarked, with easy candor.    1897 Kipling Capt. Cour. 21 You've turned up, plain, plumb providential for all concerned.    1901 F. Norris Octopus i. iii. 121 ‘I'll get plumb out of here,’ he trumpeted. ‘I won't stay here another minute.’    1926 ‘R. Crompton’ William—the Conqueror v. 89 Poor woman! She's sure plumb crazy!    1934 A. Christie Murder on Orient Express ii. ix. 136 ‘You are sure of that, M. Hardman?’ ‘I'm plumb certain.’    1967 G. F. Fiennes I tried to run a Railway vii. 76 In his presence I was tense, tongue-tied and often plumb stupid.    1973 E. Lemarchand Let or Hindrance xiv. 182 They must both be plumb crazy.

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The 1587 plum ripe looks like a different expression, arising from a comparison with ripe plums falling off a tree. – Peter Shor Jun 15 '11 at 14:12
@Peter: I agree. See the second edit to my answer. – Callithumpian Jun 15 '11 at 15:37
@Peter: The 1587 usage is still consistent with the meaning "completely," as in "completely ripe." Here's the full text of the quotation: [books.google.com/… – Simon Jester Jun 15 '11 at 16:57
It's also quite consistent with the meaning "ripe like a plum," and given the 200-year gap between that and the next occurrence, I don't trust it. – Peter Shor Jun 15 '11 at 17:26

Just an interesting observation: lead causes people to "go crazy", so "plumb crazy" could initially have referred to just that-- the craziness caused by excessive exposure to lead.

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User Callithumpian's answer above states:

Etymonline indicates that the "completely" sense of the word was an extension of the "exact measurement" sense of the word and dates this shift back to the mid-18th

So I thought to enlarge the necessary previous step: how plumb meant "exact measurement". Each indent signifies a response to an earlier post; I omit the usernames for readability.

[Source:] The periodic table's symbol for lead is Pb. Pb comes from the Latin name for lead which is plumbum. Sewage and water pipes used to be made out of lead, hence the occupation of a plumber.

This is also where we get the term plumb to mean vertical or straight down/up - a lead weight at the bottom on a string was used to find the vertical placement of walls or other features.

A plumb bob!

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Plumb is also commonly used in Britain in the phrase the plumb spot, i.e., the best possible position: e.g., in golf, I dropped the ballon the green in the plumb spot to sink it in one, or I've got seats in a plumb spot to see the match. However, it's a bit old fashioned now – tends to be used by middle aged and older people. But, hey, maybe it will come back into fashion again like cool (coined in the 1940s/50s, I believe, by the "hip cats"!).

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You may be thinking of plum. – MετάEd Jan 24 '12 at 23:53
What @MετάEd said. Would Jay speak of landing a plumb job? – FumbleFingers May 31 '14 at 20:55

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