From Longman Dictionary of Contemporary Englishwait up phrasal verb1SLEEPto wait for someone to return before you go to bed forDon’t wait up for me; I may be late.2Wait up! American EnglishWAIT used to tell someone to stop, so that you can talk to them or go with them‘Wait up!’ he called. →wait→ See Verb table
Examples from the Corpus
wait up• I'll be home late tonight, so don't wait up.• Julie's parentswaited up all night but she never came home.• I should go - Marie will be waiting up for me.• Wait up, you guys! I can't walk that fast.wait for• Uncle Vernon had waited up for her.• I would wait up for him.• Don't wait up for me - I'll be very late.• He could be waiting up for me.• The Copleys won't have waited up for me.• It cockily waited up for them, then deftly sidestepped as the three came near it once again.