Duke in a hole before Xmas (6)
I believe the answer is:
advent
'xmas' is the definition.
The definition and answer can be both related to time as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'duke in a hole before' is the wordplay.
'duke' becomes 'd' (abbreviation).
'in' is an insertion indicator.
'hole before' becomes 'vent' (vent is a kind of hole. I am not sure about the 'before' bit.).
'a'+'vent'='avent'
'd' placed into 'avent' is 'ADVENT'.
Can you help me to learn more?
(Other definitions for advent that I've seen before include "Time approaching Christmas" , "approach" , "Christmas shopping time in" , "Season preceding Christmas" , "The coming of a religous period?" .)