Day ultimately spent on wine and port (8)
I believe the answer is:
montrose
'port' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'day ultimately spent on wine' is the wordplay.
'day' becomes 'mon' (abbreviation for Monday).
'ultimately' suggests the final letters.
'on' is a charade indicator (letters next to each other).
'wine' becomes 'rose' (rose wine is a kind of wine).
The final letter of 'spent' is 't'.
'mon'+'t'+'rose'='MONTROSE'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for montrose that I've seen before include "Coastal town in Angus" , "Scottish coastal town" , "Scottish resort" .)