Cheerful Bishop Tim is tickling midriff (10)

I believe the answer is:

optimistic

I'm a little stuck... Click here to teach me more about this clue!

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

'bishop tim is tickling midriff' is the wordplay.
'OPTIMISTIC' is hidden within the letters.
But, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for optimistic that I've seen before include "Hopeful about the future" , "Looking on the bright side" , "Pollyannaish" , "Hopeful and confident" , "Happy-go-lucky" .)

I've seen this clue in the Sydney Morning Herald.

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