a. [ L. proclivis sloping, inclined; pro forward + clivus hill: cf. F. proclive. See Declivity, and cf. Proclivous. ] Having a tendency by nature; prone; proclivous. [ R. ] Mrs. Browning. [ 1913 Webster ]
(adj) descriptive of any event or stimulus or process that has an effect on events or stimuli or processes that occur subsequently, Ant. retroactive, Example:proactive inhibition; proactive interference