That can be vanquished; defeatable, conquerable.(adjective)
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Use "vanquishable" in a sentence
"He scorns all that are so silly to _trust_ [53] him, and only not scorns his enemy, especially if as bad as himself: he fears him as a man well armed and provided, but sets boldly on good natures, as the most vanquishable."
"But prejudices of taste, likings and dislikings, are not always vanquishable by reason; so, to escape the serenade from the tree, which promised to be of considerable duration"
"Had I been a Papist, I should not have wished for a more vanquishable opponent in controversy."