Clever -- going naked for shower (4)
I believe the answer is:
rain
'shower' is the definition.
(synonyms)
'clever going naked' is the wordplay.
'clever' becomes 'brainy' (I've seen this before).
'going naked' means to look at the middle letters (the word stripped of its outside letters).
The middle of 'brainy' is 'RAIN'.
'for' acts as a link.
(Other definitions for rain that I've seen before include "Precipitation" , "The right" , "eg A shower" , "Storm" , "Fall wetly" .)