Simple past tense and past participle of unring.(verb)
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Use "unrung" in a sentence
"Violations of the constitution that have already occurred won't be prosecuted because the cases will be dismissed as a result of this law -- that bell cannot be unrung."
"TT it can be done, the bell can be unrung, if Geoff backed up the old template as the download advised."
"The slur will stay with us, the proverbial bell that can't be unrung."