Acting brethren, given top half, fit uniform (7)
I believe the answer is:
equable
'uniform' is the definition.
(thesaurus)
'acting brethren given top half fit' is the wordplay.
I cannot really see how this works, but
'fit' could be 'able' (similar in meaning) and 'able' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for equable that I've seen before include "Good-natured" , "Cool" , "Calm, even-tempered" , "Not extreme" , "not easily rattled" .)