Adult insect? The writer's not entirely enthralled (5)
I believe the answer is:
imago
'adult insect?' is the definition.
(I've seen this in another clue)
'writer's not entirely enthralled' is the wordplay.
'writer's' becomes 'I'm' ('I am' referring to the writer of the clue).
'not entirely' means to remove the last letter (most but not all of the word).
'enthralled' becomes 'agog' (I've seen this in another clue).
'agog' with its final letter taken away is 'ago'.
'im'+'ago'='IMAGO'
'the' acts as a link.
(Other definitions for imago that I've seen before include "Last stage of adult insect" , "Adult, post-metamorphosis insect" , "Last state of insect life" , "being immature?" , "subconscious view" .)