Crossword Genius

Optimistic conductor may begin with this

Ross

I believe the answer is:

upbeat

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'optimistic' is the definition.
(similar in meaning)

I cannot understand how the remainder of the clue works.

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(Other definitions for upbeat that I've seen before include "Cheerful and encouraging, like lively music" , "Cheerfully optimistic" , "Optimistic - anacrusis" , "Optimistic, positive" , "Heartening" .)

I've seen this clue in The Daily Mail.
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