Here’s a modern linguistic term that I really like. An eggcorn is a word or phrase created by mishearing or misinterpreting another. An element of the original is replaced by something that sounds very similar. To be an eggcorn, the word or phrase must sound similar (or identical) to the original and make some sort of sense.
An eggcorn that I have already posted about is on tenderhooks (for on tenterhooks).
If you say ‘acorn’ in a slow drawl (as in the southern US), you will probably find that it sounds a lot like ‘eggcorn’. The spelling eggcorn goes back as far as 1844. It makes sense when you think about it – acorns look a bit like eggs, especially in their cups, and they are produced by a tree while an egg is produced by a chicken or other egg-laying animal (although not in the same way).
‘Egg corn’ was adopted in 2003 by the linguist Geoffrey Pullum as the term for misheard words/phrases of this type. Because it describes a category of words that it is a member of, it is autological.
Source: Fowler’s Dictionary of Modern English Usage, Jeremy Butterfield (editor).