The Collaborative International Dictionary of English v.0.48:
Withstander \With*stand"er\, n. One who withstands, or opposes; an opponent; a resisting power. [1913 Webster]WordNet (r) 3.0 (2006):
withstander n 1: an opponent who resists with force or resolution; "obstinate withstanders of innovation" 2: a fighter who holds out against attack [syn: defender, withstander]