R0198100 (rĕt′rō-ăk′shən)n.1. Application of a subsequent rule or condition to something that occurred at a previous time.2. An opposing or reciprocal action; a reaction.ret′ro·act′ v.
retroact
(ˈrɛtrəʊˌækt) vb (intr) 1. to act in opposition2. to influence or have reference to past events
ret•ro•act
(ˈrɛ troʊˌækt)
v.i. 1. to act in opposition; react. 2. to have reference to or influence on past occurrences. [1785–1795]