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Phrase(s): (I) beg your pardon, but... [and] Begging your pardon, but...
Please excuse me, but. (A very polite and formal way of interrupting, bringing something to someone’s attention, or asking a question of a stranger.) • Rachel: Beg your pardon, but I think your right front tire is a little low. Henry: Well, I guess it is. Thank you. • John: Begging your pardon, ma’am, but weren’t we on the same cruise ship in Alaska last July? Rachel: Couldn’t have been me.
McGrawhill's American Idioms And Phrasal Verbs