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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.
drop inalso drop by
to visit briefly About 100 guests dropped in to celebrate the publication of his book.
1. To let something fall into some other thing: I dropped some spare change in the beggar's cup. I took some rocks to the hole and dropped them in. Don't push the latch down into the lock; just let it drop in.
2. To come to some place for a casual visit: We'll drop in and see how you're doing tomorrow. Should we drop in on our neighbors tonight?