ˈaktəˌvād.ə(r) noun
( -s )
: one that activates: as
a. : a substance that renders another substance active in a specific manner: as
(1) : a chemical (as an ethanolamine) that acts with an accelerator to increase the rate of vulcanization of rubber
(2) : an impurity (as a metal) present in small amounts in a luminescent solid (as a phosphor) to which the luminescence is attributed
(3) : a substance (as a chloride ion) that increases the activity of an enzyme — usually distinguished from coenzyme and kinase
b. embryology : a substance given off by developing tissue that stimulates differentiation of adjacent tissue ; also : a structure giving off such a stimulant
c. : accelerator 1b