reaction

re- (Latin)

Again; prefix added to various words to indicate an action being done again, or like the other usages indicated above under English.. Back, backwards.

agendum (Latin)

reago (Latin)

reactio (Latin)

(physics, chemistry) reaction.

reaction (Old French)

reaction (English)

(chemistry) A transformation in which one or more substances is converted into another by combination or decomposition. An action or statement in response to a stimulus or other event.