Active  —adj. 1 marked by action; energetic; diligent (an active life). 2 working, operative (active volcano). 3 not merely passive or inert; positive (active support; active ingredients). 4 radioactive. 5 gram. Designating the form of a verb whose subject performs the action (e.g. Saw in he saw a film). —n. Gram. Active form or voice of a verb.  actively adv. [latin: related to *act]