Sailor isn't entertaining creature of the night (5)
I believe the answer is:
loris
'creature of the night' is the definition.
(Loris matches up with the definition creature of the night)
'sailor isn't entertaining' is the wordplay.
'entertaining' indicates a hidden word.
'LORIS' can be found hidden inside 'sailor isnt'.
(Other definitions for loris that I've seen before include "Slow-moving nocturnal primate" , "Small nocturnal primate" , "Short-tailed mammal" , "lemur" , "Nocturnal primate of Southeast Asia (usually slender or slow)" .)