This post will deal with true Folk Etymology, where an unfamiliar word is changed into a more familiar form, or as Anatoly Lieberman puts it in
Word Origins...and how we know them "the process of altering otherwise incomprehensible words, in order to give them a semblance of meaning". The other sense of Folk Etymology (called "Etymythology" by Michael Quinion in his book
POSH) in which people make up plausible origins of words or phrases, was discussed in a previous post July 13.

There are two sources of unfamiliar words -- old words that have lost their meaning over time, and new words borrowed from another language. An oft quoted example of the former is
bridegroom. The original was
bridegome where
gome was an Old English word for "man". By the 16th century
gome had fallen out of use, remaining only in
bridegome where it no longer made sense. The more common word
groom was substituted even though at the time it referred to a manservant or person of a lower class (the horse keeper sense of
groom developed more recently).
Another example is
kitty-corner for diagonally opposite. The original was
cater-corner where
cater is an English word meaning "four" Anglicized from the French
quatre.
Cater developed into a verb meaning "to place diagonally".
Cater is now rarely used outside this expression, so it no longer made sense, and various versions sprang up including
catty-corner and the more familiar
kitty-corner. It is speculated that some people thought the word had something to do with prowling cats, but I don't think this is necessary at all for the word change.
Kitty-corner just seems easier to pronounce, and makes a little more sense than
cater-corner. One word that
does relate to cats that I had not suspected, is
caterpillar which is from Old French
chatepelose meaning "hairy cat".
A frequently referenced example of a word changed from a foreign language is
cockroach from Spanish
cucaracha (it was
cacarucha with the U in a different syllable at the time it was borrowed).
Cock and
roach were two familiar but unrelated English words joined to approximate the new unfamiliar word.
Sometimes the translation completely changes the meaning. In America, the French
Cap d'Espoir (Cape of Hope) was Americanized to
Cape Despair and the place name
Purgatoire (Purgatory) became
Picketwire.