ini·ti·a·tor \ə̇ˈnishēˌād.ə(r), -ātə- sometimes -isē-\noun (-s) Etymology: Late Latin, from Latin initiatus (past participle of initiare to initiate) + -or — more at initiate : one that initiates: as a.: a person who originates or sets on foot some process or movement < a great initiator in art > b.: detonator c c.: a substance that initiates a reaction < benzoyl peroxide is used as an initiator in polymerization > — compare catalyst 1