Senior officer keeping it back for hearing? (4)
I believe the answer is:
otic
'hearing?' is the definition.
(thesaurus)
'senior officer keeping it back' is the wordplay.
'senior officer' becomes 'co' (commanding officer**).
'keeping' indicates putting letters inside.
'back' is a reversal indicator.
'co' going around 'it' is 'cito'.
'cito' backwards is 'OTIC'.
'for' is the link.
(Other definitions for otic that I've seen before include "organ" , "Relating to ears" , "of concern to the listener" , "about hearing" , "in relation to the listener" .)