Pronunciation: (ak'tu-vist), [key]
an especially active, vigorous advocate of a cause, esp. a political cause.
1. of or pertaining to activism or activists: an activist organization for environmental concern.
2. advocating or opposing a cause or issue vigorously, esp. a political cause: Activist opponents of the President picketed the White House.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.