militant

Etymology

From Middle French militant, from Latin mīlitāns, present participle of mīlitāre (“to serve as a soldier”).

adj

1. Fighting or disposed to fight; belligerent, warlike.
   The upper tiers of the foreign ministry were quick to embrace a militant policy. 2012, Christopher Clark, The Sleepwalkers, Penguin, published 2013, page 394
2. Aggressively supporting of a political or social cause; adamant, combative.

noun

1. (obsolete) A soldier, a combatant.
2. An entrenched or aggressive adherent to a particular cause, now especially a member of a particular ideological faction.
   Officials in Pakistan have confirmed that at least 250 schoolchildren between 12 and 18 years old and several teachers were taken hostage by at least seven militants inside a high school in Domail. 2008, Militants in Pakistan release 250 schoolchildren after taking them hostage, Wikinews
3. (specifically, communism) someone who supports the Trotskyist political view expressed in the newspaper Militant, or who engages in aggressive left-wing politics.