Sense crew's keeping OK (8)
I believe the answer is:
eyesight
'sense' is the definition.
(eyesight is a kind of sense)
'crew's keeping ok' is the wordplay.
'crew' becomes 'eight' (I've seen this before).
'keeping' means one lot of letters goes inside another.
'ok' becomes 'yes' (I've seen this before).
'eight' going around 'yes' is 'EYESIGHT'.
(Other definitions for eyesight that I've seen before include "Perceptive faculty" , "Purpose of certain organs" , "Ability to see" , "Seeing faculty" , "Requirement to look" .)