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general::
Phrase(s): drop in (on someone) [and] drop in (to say hello)
to pay someone a casual visit, perhaps a surprise visit. • I hate to drop in on people when they aren’t expecting me. • You’re welcome to drop in at any time., Phrase(s): drop in (to say hello)
Go to drop in (on someone).
McGrawhill's American Idioms And Phrasal Verbs