Fancies a drink when in semi-retirement (8)
I believe the answer is:
imagines
'fancies' is the definition.
(I've seen this before)
'a drink when in semi-retirement' is the wordplay.
'drink' becomes 'gin' (gin is a kind of drink).
'when in' means one lot of letters goes inside another.
'retirement' is a reversal indicator (retire can mean to return or go back).
'semi' back-to-front is 'imes'.
'a'+'gin'='agin'
'agin' going within 'imes' is 'IMAGINES'.
(Other definitions for imagines that I've seen before include "Fancies" , "Conceives in the mind" , "Supposes" , "Conjures up in the mind" , "Forms an idea of" .)