A regular at Christmas giving you permission for a kiss? (9)
I believe the answer is:
mistletoe
'a regular at christmas' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'permission for a kiss?' is the wordplay.
I cannot really understand how this works, but
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is located in the answer.
This explanation may well be incorrect...
'giving you' is the link.
(Other definitions for mistletoe that I've seen before include "Stole mite from the Christmas plant" , "White-berried parasite" , "put up for a Christmas function?" , "Christmas berry" , "Parasitic plant" .)