They're up for approval (6)
I believe the answer is:
thumbs
'they're up' is the definition.
The definition suggests an adverb but the answer is not.
'approval' is the wordplay.
I cannot quite understand how this works, but
'approval' could be 'mb' (MB is an example) and 'mb' is found in the answer.
The remaining letters 'thus' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for thumbs that I've seen before include "Hitches a lift" , "To be all these is to be clumsy" , "reads intensively" , "Short thick digits" , "Digits; requests (lift)" .)