Definitions
American Heritage® Dictionary of the English Language, Fourth Edition
- v. To attack as false or questionable; challenge in argument: impugn a political opponent's record.
Century Dictionary and Cyclopedia
- To attack by words or arguments; contradict; assail; call in question; gainsay.
Wiktionary
- v. To assault, attack.
- v. To verbally assault, especially to argue against an opinion, motive, or action; to question the truth or validity of.
GNU Webster's 1913
- v. To attack by words or arguments; to contradict; to assail; to call in question; to make insinuations against; to gainsay; to oppose.
WordNet 3.0
- v. attack as false or wrong
Etymologies
- Middle English impugnen, from Old French impugner, from Latin impugnāre : in-, against; see in-2 + pugnāre, to fight; see peuk- in Indo-European roots.
Examples
“Wunderman said he didn't want to "impugn" the motives of officials in those cities, acknowledging they were serving the needs of their constituents.”
Jacksonville Business News - Local Jacksonville News | Jacksonville Business Journal
“The narrator doesn't impugn the behavior of man who fired his father for falling asleep on the job.”
The Huffington Post: Richard B. Woodward: We The Animals: Novel Of The Year?
“I don't think it's useful to impugn her motives; I think it's more useful to address her argument.”
GUEST POST: Jennifer Brissett Weighs in on the Writer Pay Rate Flap
“In a world in which God brought only good things, what would not impugn His goodness?”
“Meanwhile you make completely unsupported claims all over the place, and yet impugn my intellectual honesty.”
“If you are going to impugn the character of respected scientists, then we need some evidence other than a bald assertion.”
Matthew Yglesias » January Was the Warmest Temperature in World History
“While he notes that there are "patriotic reasons for strongly opposing higher tax rates," it is quite obvious that wealthy conservatives like Mr. Moore have compelling personal reasons for opposing them, too, and hence perfectly understandable why they might want to counter the perception that they are merely selfish and greedy by trying to impugn the character of those who disagree with them rather than focusing on the substance of our position.”
The Huffington Post: Eric Schoenberg: The Hypocritical Oath?
“Then again - not to impugn you, Leigh, or any of the readers/commenters - there is a degree to which our own cynicism determines whether we view a particular emotional expression as contrived or not.”
“Democrats in Texas are trying to stir things up by using half quotes to impugn his character, Sullivan said.”
The Huffington Post: Ron Paul, In 1996, 'Did Not Deny' Controversial Statement In Newsletter
Lists
These user-created lists contain the word ‘impugn’.
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GRE Barrons Wordlist
A complete Barron's Wordlist for GRE preparation. Your online flashcard replacement.
abase, abash, abate, abbreviate, abdicate, aberrant, aberration, abet, abeyance, abhor, abject, abjure and 4084 more...
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SAT Words
But only the ones that I don't already know.
abase, abash, abominate, abstruse, acclivity, accolade, accost, adroit, adulate, adulterate, adumbrate, affray and 241 more...
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Words build meanings from origins( etymology )
These come from gamma meditation ,I think.
discursive, exogenous, machinations, purportedly, sumptuous, congruity, cantankerous, incongruous, festoon, hessian, ratiocinative, stratigraphic and 837 more...
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GRE Study guide
Going through the Magoosh website, words I pulled from the verbal section. 2012.
magnanimous, correlate, anglicized, simulacrum, tantamount, obsequiousness, subterfuge, vehement, vociferous, benign, concomitant, veracity and 83 more...
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Censure (v.)
Someone must have had an inferiority complex.
vituperate, vilify, trounce, traduce, slander, scold, revile, reprove, reprimand, reprehend, remonstrate, rebuke and 37 more...
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November
irresolute, obsequious, truculent, palliative, salvo, troubadour, elocutionist, pseudepigraphy, abattoir, repudiate, impugn, vitiated and 3 more...

Dan337
It appears (from, e.g., almost every sentence cited on the first page of usage examples for “impune”*) that almost every person who writes the word “impune” in English intends the word “impugn”.* The only two exceptions use the word in the Latin† motto “Nemo me impune lacessit” (or a fragment thereof).
† That is to say the language of the motto is Latin; it’s the motto of the Order of the Thistle, a chivalric order associated with Scotland. Jan 6, 2011
sonofgroucho Great word: not used nearly often enough. I feel as if it should be connected with impunity, but it doesn't seem to be. Nov 11, 2007