A mostly gloomy outlook primarily for drink (7)
I believe the answer is:
amoroso
'drink' is the definition.
(type of sherry)
'a mostly gloomy outlook primarily' is the wordplay.
'mostly' means to remove the last letter.
'gloomy' becomes 'morose' (I've seen this before).
'primarily' suggests taking the first letters.
The initial letter of 'outlook' is 'o'.
'morose' with its last letter removed is 'moros'.
'a'+'moros'+'o'='AMOROSO'
'for' acts as a link.
(Other definitions for amoroso that I've seen before include "Loving, tender (in music)" , "tenderly" , "Dark sweet sherry" , "Play lovinglly" , "He loves" .)