I've seen the expression "to do someone in" for the first time today and from what I found, it means "to kill someone." Where does it come from?

The trailing "in" implies something following and makes the expression sound incomplete.

  • The actual preposition "in" is arbitrary. In fact it looks like do someone up was around earlier, but that version sounds really odd to my modern ear. The earlier instances in that link are predominantly American, but my gut feeling is to agree with @Aaron that the in version sounds more Cockney than Yankee. Jul 4, 2013 at 21:47
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    In latin, interficere (litt. "do into") means "to kill" too.
    – user109759
    Feb 16, 2015 at 9:24

2 Answers 2


I'm sure the origin can be argued, but this almost certainly came from the east end of London.

When you say 'do him' or 'he did him' it means to beat someone up. So 'do him in' goes further.

Other common cockney phrases are 'Kick his head in' or 'punch his face in' so it only makes sense.

'In' being invasive, meaning entering inside, which is generally how you kill someone.

Coming from London myself it seems perfectly normal to to use 'in'.

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    +1. It was 'cockney slang' when Shaw wrote Pygmalion; I doubt whether further sleuthing would be worthwhile. Jul 4, 2013 at 21:24
  • @Aaron The word 'in', with the definition you gave seems to fit, and brings more sense to the expression. I still think that it doesn't match up really well with the verb 'do' as opposed to 'kick' or 'punch', or could use some complements. (Maybe that's just because English isn't my native language.)
    – user36216
    Jul 4, 2013 at 22:01
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    @KaivoAnastetiks You may not think " it ... match[es] up really well with the verb 'do'" - but that is the expression, and similar comments could be made about prepositional use in very many English expressions. But the only rule is that "there ain't no rules" and many uses just have to be accepted as 'that is the way it's developed', and 'that is the way it is'!
    – TrevorD
    Jul 4, 2013 at 23:01
  • Hmm. Most of these (except for "do him" w/o the "in") sound fine in US-EN, too. This is interesting and plausible, but I'm not wholly convinced. I can't do better, but I'd like to see someone else try (or at least have a more thorough/cited version of this).
    – hunter2
    Jul 5, 2013 at 7:14

I looked up the meaning of this expression as it is part of the Eliza Doolittle conversation during the Ascot Race scene. The British 'aristocrats' don't understand the expression and ask for the meaning. Professor Higgins has to explain it.In the context of the hilarious sketch, it is clear that the expression is 100% Cockney.


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