Medusa could be entertained (6)
I believe the answer is:
amused
'entertained' is the definition.
(amusing is a kind of entertaining)
'medusa could be' is the wordplay.
'could be' is an anagram indicator.
'medusa' is an anagram of 'AMUSED'.
(Other definitions for amused that I've seen before include "Mildly diverted or entertained" , "Victoria reputedly wasn't" , "Kept someone entertained" , "Delighted" , "Queen Victoria wasn't!" .)