I stumbled about the curious fact that a word such as foot meaning lower part of the leg can develop a totally different meaning such as 'nonsense'. Another curious fact is the use of 'my'. I would like to propose the possibility that 'foot' in the expression 'my foot' is connected with French foutaise meaning nonsense. The French word was shortened and transformed to the already existing word 'foot', even if that doesn't make any sense. As I found no etymological explanation of 'My foot' I think the connection with foutaise has a high probability. The Online Etymology Dictionary says: Quote: Colloquial exclamation my foot! expressing "contemptuous contradiction" [OED] is first attested 1923, probably a euphemism for my ass, in the same sense, which dates back to 1796. From Online Etymology Dictionary. The use of the word 'probably' indicates that there is quite an amount of uncertainty. A euphemism is no etymological explanation. The question would remain: Where does this euphemism come from? But the reference to 'my ass' could explain the use of 'my' - an analogy to an expression of similar meaning. Normally a word meaning lower part of the leg does not develop a use with totally different meaning such as 'nonsense'. That is not in the line of semantic developments. If such jumps were possible the speakers would not understand their language any more after some time. Even semantic developments have a certain logic, even if that logic can get lost in the course of centuries. The Oxford Dictionary of English (the one-volume edition, 3rd edition of 2010) has 'my foot!' in the normal entry 'foot'. It would be preferable to have a second entry: foot (2) with the expression 'my foot', simply because it has a totally different source and nothing to do with 'foot' (part of the leg).
I present these ideas here on the page of discussion, because I'm not used to writing articles for Wikipedia or Wiktionary. The formalities are much too complicated for me. So if this contribution is interesting for Witionary, please write it in the appropriate form. --Rogermue 12:36, 24 April 2011 (UTC)
Could it not be a contraction from 'I put my foot down'? It already holds the sentiment of opposition and contempt, and frankly makes sense. (I have never contributed to a talk page so I don't know thee protocol-James, not a proper member, 23/03/2013)
I disagree that a euphemism isn't an explanation. "My foot" rolls of the tongue well.