Retro-. [L. retro, adv., backward, back. Cf. Re-.] A prefix or
combining form signifying backward, back; as, retroact, to act
backward; retrospect, a looking back.
Re`tro*act" (?), v. i. [Pref. retro- + act.] To act backward, or in
return; to act in opposition; to be retrospective.
Re`tro*ac"tion (?), n. [Cf. F. rétroaction.] 1. Action returned, or
action backward.