abyss

\ \ [16] English borrowed abyss from late Latin abyssus, which in turn derived from Greek ábussos. This was an adjective meaning ‘bottomless’, from a- ‘not’ and bussós ‘bottom’, a dialectal variant of buthós (which is related to bathys ‘deep’, the source of English bathyscape). In Greek the adjective was used in the phrase ábussos limnē ‘bottomless lake’, but only the adjective was borrowed into Latin, bringing with it the meaning of the noun as well.

\ \ In medieval times, a variant form arose in Latin – abysmus. It incorporated the Greek suffix -ismós (English -ism). It is the source of French abîme, and was borrowed into English in the 13th century as abysm (whence the 19th-century derivative abysmal). It began to be ousted by abyss in the 16th century, however, and now has a distinctly archaic air.