impugn (v.)

"attack by argument," late 14c., from Old French impugner (14c.), from Latin impugnare "to fight against, assault, attack," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + pugnare "to fight" (see pugnacious). Related: Impugned; impugning. Impugnable has meant "liable to be assailed" (1823) and "that cannot be assailed" (1560s).