From Longman Dictionary of Contemporary Englishsundaesun‧dae /ˈsʌndeɪ $ -di/ noun [countable] 
DFFa dish made from ice cream, fruit, sweet sauce, nuts etc a chocolate sundae
DFFa dish made from ice cream, fruit, sweet sauce, nuts etc a chocolate sundaeExamples from the Corpus
sundae• A sundae?-All right.-Hot fudge?-I guess.• She has a job frying hamburgers at Hooks Drugstore, where she is also learning to make sodas and sundaes.• a hot fudge sundae• Mr. Boni's Restaurant T-bone steaks, giant burgers, pizzas and outrageous sundaes.• Thanks, Brice.-Thank you for the sundae, Mr Calder, I said.• You go get the sundae first.• The chopped nuts on the sundae are the husband-and-wife team who present the show.Origin sundae (1800-1900) Probably from Sunday 