late 14c., "action of adding numbers;" c. 1400, "that which is added," from Old French adition "increase, augmentation" (13c.), from Latin additionem (nominative additio) "an adding to, addition," noun of action from past-participle stem of addere "add to, join, attach" (see add). Phrase in addition to "also" is from 1680s.
1550s, in grammar, "addition of a letter or syllable to a word," from Late Latin, from Greek prosthesis "a putting to, an addition," from prostithenai "add to," from pros "to" (see pros-) + tithenai "to put, to place" (from reduplicated form of PIE root *dhe- "to set, put").
From 1706 in medical arts as "the addition of an artificial part to supply a defect of the body" on the notion of "that which is added to" the body. The sense was extended to "artificial body part" by 1900. Plural prostheses.
1610s, "pertaining to connotation," from Medieval Latin connotativus, from past-participle stem of connotare "to signify in addition to the main meaning;" see connotation. Meaning "implying an attribute while denoting a subject" is from 1829 (J.S. Mill).