Present participle of regret. Also form regreting is used, although it is not generally recognized by dictionaries.(verb)
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Use "regretting" in a sentence
"Not yet can I speak with the authority of the "retired" from labour, a shadowy company who spend their time in regretting their retirement and in criticising their successors."
"He persisted only in regretting that he had failed to clean his honour, and died impenitent."
"You’ve given so much attention to this beleaguered 3L but not a word regretting the fate of Mr. Jones, it seems."