A person who withstands or resists; an opponent(noun)
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Use "withstander" in a sentence
"Remember what I told you: this wealthy franklin is proud, fierce, jealous, and irritable, a withstander of the nobility, and even of his neighbors, Reginald Front-de-Boeuf and Philip Malvoisin, who are no babies to strive with."
"O thou withstander of all foes, igniting the sacred fire, take thou her hand with due rites. '"
"His father is a stout withstander of the Scots, and the earl would have given him knighthood, if he would have taken it; and maybe, in the future, the son will win that honour."