Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
plenitude, plentitude (nn.)
Both mean “an abundance, a great sufficiency,” but plenitude is the word to use. Plentitude is a rare variant, perhaps originally an error or a misprint or else made with plenty in mind, rather than the Latin plenus “full,” which gives us plenitude. Plentitude occurs so seldom that most Standard users consider it a mistake.
