militant (n.) Look up militant at Dictionary.com
"one engaged in war or strife," c. 1600, from militant (adj.); in a political sense, it is attested by 1907.
militant (adj.) Look up militant at Dictionary.com
early 15c., "fighting, engaged in warfare," from Middle French militant "fighting," from Latin militantem (nominative militans), present participle of militare "serve as a soldier" (see militate), originally especially in Church militant. Related: Militantly.