militant
Concise Oxford English Dictionary © 2008 Oxford University Press:
militant/ˈmɪlɪtənt/
▶adjective favouring confrontational methods in support of a cause. ▶noun a militant person.
– derivatives
militancy noun,
militantly adverb.
militancy noun,
militantly adverb.
– origin ME (in the sense ‘engaged in warfare’): from OFr., or from L. militant-, militare (see militate).
'militant' also found in these Oxford entries:

