Adjective upbeat has 1 sense
- cheerful, pollyannaish, upbeat - pleasantly (even unrealistically) optimistic
Antonym: pessimistic (indirect, via optimistic)
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Noun upbeat has 2 senses
- wellbeing, well-being, welfare, upbeat, eudaemonia, eudaimonia - a contented state of being happy and healthy and prosperous; "the town was finally on the upbeat after our recent troubles"
--1 is a kind of prosperity, successfulness
--1 has particulars: fool's paradise; health, wellness
- upbeat - an unaccented beat (especially the last beat of a measure)
--2 is a kind of rhythm, beat, musical rhythm
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