That lessens the seriousness of something by providing an excuse(adjective)
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Use "extenuating" in a sentence
"There may be what you call extenuating circumstances -- though I can't quite imagine it."
""If you had been innocent -- even if there had been what they call extenuating circumstances -- I would have spent a fortune in the endeavor to set you free; but your confession renders me powerless.""
"This law simply gives the police authority in extenuating circumstances during the course of a routine stop (traffic violation, etc)."