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Phrase(s): mull something over
to think about something; to ponder or worry about something. • That’s an interesting idea, but I’ll have to mull it over. • I’ll mull over your suggestions and reply to you next week.
McGrawhill's American Idioms And Phrasal Verbs
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Ponder, think about, as in She mulled over the offer for some time and then turned it down. [Late 1800s]
American Heritage Idioms