noun. An unaccented beat or beats that occur before the first beat of a measure.

noun. The upward stroke made by a conductor to indicate the beat that leads into a new measure.

adjective. Optimistic.

adjective. Happy; cheerful.

adjective. Having a fast pace, tempo, or beat.

adjective. Having a positive, lively, or perky tone, attitude, etc.

noun. An unaccented beat at the start of a musical phrase.

adjective. pleasantly (even unrealistically) optimistic

noun. an unaccented beat (especially the last beat of a measure)

noun. a contented state of being happy and healthy and prosperous

"Then again, what you refer to as "upbeat" we might describe as "frenzied.""

downbeat  

optimistic  

beat  musical rhythm  rhythm  

ambivalent  approachable  bouncy  buoyant  carefree  

Great Leap Forward  Leibnizian  advance  advancement  amelioration