adultery

\ \ [14] Neither adultery nor the related adulterate have any connection with adult. Both come ultimately from the Latin verb adulterāre ‘debauch, corrupt’ (which may have been based on Latin alter ‘other’, with the notion of pollution from some extraneous source). By the regular processes of phonetic change, adulterāre passed into Old French as avoutrer, and this was the form which first reached English, as avouter (used both verbally, ‘commit adultery’, and nominally, ‘adulterer’) and as the nouns avoutery ‘adultery’ and avouterer ‘adulterer’.

\ \ Almost from the first they coexisted in English beside adult- forms, deriving either from Law French or directly from Latin, and during the 15th to 17th centuries these gradually ousted the avout- forms. Adulter, the equivalent of avouter, clung on until the end of the 18th century, but the noun was superseded in the end by adulterer and the verb by a new form, adulterate, directly based on the past participle of Latin adulterāre, which continued to mean ‘commit adultery’ until the mid 19th century.

\ \ Cf.⇒ ALTER