An amoeba is a formless thing ...

An amoeba is a formless thing which takes many shapes. It moves by thrusting out an arm, and flowing into the arm. It multiplies by pulling itself in two, without permanently diminishing the original. So with words. A meaning may develop on the periphery of the body of meanings associated with a word, and shortly this tentacle-meaning has grown to such proportions that it dwarfs all other meanings.
 Charlton Laird

Quotes from the same author

Jazz was formerly a crude term for indulging in an action which in polite society is referred to, if at all, only with such vague Latin terms as intercourse and cohabitation.
 Charlton Laird