Fruit cocktail guzzled up partially (4)
I believe the answer is:
ugli
'fruit' is the definition.
(I know that Ugli is a fruit)
'cocktail guzzled up partially' is the wordplay.
'partially' indicates the answer is hidden within the clue.
'up' is a reversal indicator (in down clue: letters go upwards).
'ilgu' is hidden in the letters of 'cocktail guzzled'.
'ilgu' back-to-front is 'UGLI'.
(Other definitions for ugli that I've seen before include "Mottled tangelo hybrid" , "Unattractive-sounding fruit?" , "Tropical fruit" , "Plain-sounding fruit" , "Trademark name for a hybrid citrus fruit" .)