The word eggcorn was coined collectively by the linguists who write at the excellent group blog Language Log.
Linguists collect usage examples. Unlike language teachers or the often
self-styled grammar experts who complain in the press about the decay
of English, they are not picky: the actual, real-life use is what
counts, and the most interesting bits — those that might reveal
something about how real people apprehend their language — often
stretch the received rules of correctness.
In September 2003, Mark Liberman reported (Egg corns: folk etymology, malapropism, mondegreen, ???)
an incorrect yet particularly suggestive creation: someone had written
“egg corn” instead of “acorn”. It turned out that there was no
established label for this type of non-standard reshaping. Erroneous as
it may be, the substitution involved more than just ignorance: an acorn
is more or less shaped like an egg; and it is a seed, just like grains
of corn. So if you don’t know how acorn is spelled, egg corn actually makes sense.
Other examples of eggcorns are:
"for all intensive purposes"
"here, here" (instead of "hear, hear")
"coming down the pipe"
The aforementioned Elizabeth gets credit for spotting a new eggcorn in common usage, and it is now included in the dictionary: "half-hazard."
Eggcorns are different from malapropisms, which can also be fun to watch for. A malapropism is a word used in place of the correct word, where the substitution sounds similar to the intended word but means something vastly different, often resulting in quite comical sentences. A famous example is the line uttered by Curly of the Three Stooges: "I resemble that remark!"
(The link takes you to WikiPedia, where there are many more examples of malapropisms and eggcorns, including a malapropism that made me laugh out loud: "New Scientist also reported the first-ever malapropism for
"malapropism", when, having become aware of his error, the office
worker apologized, saying he had committed a "Miss Marple-ism." No doubt he was thinking of Mrs. Malaprop, the character in Richard Brinsley Sheridan’s play, The Rivals, whose comical linguistic errors gave rise to the term.)
So a malapropism is a wrong word used in place of a word that sounds similar, but not identical, and has a totally different meaning. An eggcorn is a substitution that sounds the same or almost the same as a word or phrase—so similar, and making just enough sense, that it often passes into common usage: "blatantly obvious" instead of "patently obvious."
Don’t you just love the English language?