eggcorn

Linguist Geoffrey Pullum says, "It would be so easy to dismiss eggcorns as signs of illiteracy and stupidity, but they are nothing of the sort. They are imaginative attempts at relating something heard to lexical material already known."

See sionnach's eggcorn list

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.

quote from the Eggcorn database

Merriam-Webster Dictionary:

noun
Etymology: Middle English nekename additional name, alteration (resulting from misdivision of an ekename) of ekename, from eke eke, also + name name
Date: 15th century
1 : a usually descriptive name given instead of or in addition to the one belonging to a person, place, or thing
2 : a familiar form of a proper name (as of a person or a city)