1.  withstander(n = noun.person) - an opponent who resists with force or resolution; "obstinate withstanders of innovation"
is a kind of adversary, antagonist, opponent, opposer, resister
Derived form verb withstand₁

2.  withstander(n = noun.person) defender - a fighter who holds out against attack;
is a kind of battler, belligerent, combatant, fighter, scrapper
Derived form verb withstand₂

   One who withstands, or opposes; an opponent; a resisting power. [1913 Webster]