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I often hear phrases such as "infantry were sent in to diffuse/defuse the situation," and I am never quite sure which people are saying, and which is correct. Both seem to make sense.

To me (a chemist/physicist) the primary definition of the intransitive verb "diffuse" has a very specific meaning: to move randomly through a medium. I also understand the transitive verb "diffuse" to mean to make something less concentrated, or to lower its energy.

"Defuse," on the other hand, has one clear meaning: to remove the fuse from a bomb (or situation), making it less dangerous.

So the question is, when I hear "diffuse/defuse the situation," is there a more correct word to use, or is this a case where words are both homophones and synonyms? (Which would be pretty cool.)

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google for 'eggcorn' –  Mitch Apr 1 at 0:42
    
There's a word for it! That is what I was looking to describe. –  andyras Apr 1 at 1:28
    
In my sort of English they're also not quite homophones - the first syllable is longer in defuse. –  Chris H Apr 1 at 8:56

4 Answers 4

up vote 11 down vote accepted

Defuse the situation is the more sensible of the two:

It employs the metaphor that the situation is a bomb, and may explode. Defusing it will render it harmless.

Diffusing a situation would mean to spread it out and make it less concentrated. You can make a case that the intensity of the situation needs diffusion to make it less dangerous, but I believe it to be a stretching of the metaphor to the point where it seems to really be a mangling of defuse.

Note, both are commonly used, so it's not really wrong to use diffuse.

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I think the vast majority of uses of diffuse are intended to be defuse. Applied to an angry crowd for example either could apply - but the crowd would diffuse, defusing the situation. –  Chris H Apr 1 at 8:55
    
But "sending in infantry to diffuse the situation" might unintentionally be more accurate than the normal metaphor "defuse the situation". The effect of the infantry might be to cause the situation to affect more people over a larger area for a longer period of time! Of course when that happens, typically the intensity is not reduced in proportion and so it is not a diffusion. And if the infantry has the intended effect of ending the conflict then again it's not diffusing the situation, it's reducing/eliminating it. –  Steve Jessop Apr 1 at 11:27
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"both are commonly used, so it's not really wrong" No, diffuse is clearly wrong in this usage. Just because a lot of people are illiterate and use the wrong word or phrase, doesn't make it right. –  Phil Perry Apr 1 at 13:16
    
@Phil eventually common usage wins. And the meaning isn't that far off (per my comment above). If you said swordfish vs defuse that would be blatantly wrong. See the comment above yours. –  David M Apr 1 at 17:43

'Defuse is a verb, which means 'to remove the fuse'. But it is often used figuratively, such as in 'UN forces were sent in to help defuse the tensions between the warring parties'.

'Diffuse, is also a verb, meaning to 'spread over a wide area, or among a larger number of people' such as 'the problem is how to diffuse power without creating anarchy'. But 'diffuse' is more frequently used as an adjective meaning 'widespread', or 'not concentrated'. 'Lacking clarity, the second proposal is more diffuse'.

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According to OED, the word defuse is coined in 1943, by combining de- and fuse(v.) (which is invented in 1680s as a back-formation from fusion, a noun came from Middle French fusion, from Latin fusionem), while the verb form of diffuse is coined in 1520s from Latin diffusus, past participle of diffundere "to pour out or away".

Despite the similarities in spelling, they have different origins.

OOD suggests that defuse can be defined as "to remove the fuse from (an explosive device) in order to prevent it from exploding" and "to make (a situation) less tense or dangerous", which is pretty different from the definition of diffuse.

diffuse (v.)

  1. Spread over a wide area or between a large number of people

  2. Intermingle with another substance by movement, typically in a specified direction or at specified speed.

  3. Cause (light) to spread evenly to reduce glare and harsh shadows.

Furthermore, diffuse can also be used as an adjective.

So apparently, the expression defuse the situation makes more sense.

If you conduct a comparison in a Google Ngram, you will discover that this expression is also more widely used.

enter image description here

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Excellent tool, thanks for pointing it out. –  andyras Apr 1 at 1:27

Most importantly,

  • diffuse ends in an /s/
  • defuse ends in a /z/

If you get that straight, there will be no problems.

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That's only true of the adjective diffuse. The verb diffuse ends with /z/. –  smithkm Apr 1 at 2:53
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Yes, but the verb is very rare in practice (like the verb effect and the noun affect), and in context there's little problem, since diffuse is intransitive, while defuse is transitive. –  John Lawler Apr 1 at 3:12
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@JohnLawler Examples that Oxford Dictionaries gives of diffuse as a verb are: 'The problem is how to diffuse power without creating anarchy' and 'Oxygen molecules diffuse across the membrane'. The first of those looks like a transitive use to me. So I am slightly puzzled at your mentioning it as intransitive. –  WS2 Apr 1 at 7:55
    
I've never seen it used transitively as in the first example. It sounds odd to me, and from the fact that power is used in construction with anarchy, I deduce that it's a political metaphor, so one may reasonably wonder at its distribution. –  John Lawler Apr 1 at 14:05

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