An entrenched or aggressive adherent to a particular cause, now especially a member of a particular ideological faction.
Specifically, someone who supports the Trotskyist political view expressed in the newspaper Militant, or who engages in aggressive left-wing politics.
Fighting or disposed to fight; belligerent, warlike.
Aggressively supporting of a political or social cause; adamant, combative.
A side, party (e.g. a team or armed force) seen as adversary, enemy etc. opposite one (or more) other(s), as in a battle or team sports competition.