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Phrase(s): come Monday
Rur. when Monday comes. (Can be used with other expressions for time, as in come next week, come December, come five o’clock. See the second example.) • Joe plays so hard on the weekend that come Monday, he’s all worn out. • You may think that putting up storm windows is a bother, but come December, you’ll be glad you did it.
McGrawhill's American Idioms And Phrasal Verbs