Take care of what's kept by chum in department? (4)
I believe the answer is:
mind
'take care' is the definition.
(I've seen this before)
'what's kept by chum in department?' is the wordplay.
'what's kept by' says the answer is hidden in the clue.
'MIND' is hidden in the letters of 'chum in department'.
'of' acts as a link.
(Other definitions for mind that I've seen before include "This can be made up" , "Intelligence" , "remember" , "Brain" , "Watch - intellect" .)