to challenge as false (another's statements, motives, etc.); cast doubt upon.
2.
Archaic. to assail (a person) by words or arguments; vilify.
3.
Obsolete. to attack (a person) physically.
Origin
1325-75;Middle Englishimpugnen < Middle Frenchimpugner < Latinimpugnāre to attack, equivalent to im-im-1 + pugnāre to fight, derivative of pugnus fist; see pugnacious
C14: from Old French impugner, from Latin impugnāre to fight against, attack, from im- + pugnāre to fight
Word Origin and History for impugn
v.
"attack by argument," late 14c., from Old French impugner, from Latin impugnare "to assault, to attack," from assimilated form of in- "into, in, on, upon" (see in- (2)) + pugnare "to fight" (see pugnacious). Related: Impugned; impugning.