1530s, from French impunité (14c.) and directly from Latin impunitatem (nominative impunitas) "freedom from punishment, omission of punishment," also "rashness, inconsideration," from impunis "unpunished, without punishment," from assimilated form of in- "not, opposite of" (see in- (1)) + poena "punishment" (see penal).
"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).
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Harper, D. (n.d.). Etymology of impune. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/impune