Mad, not opening outlet in the run up to Christmas (6)
I believe the answer is:
advent
'to christmas' is the definition.
(thesaurus)
'mad not opening outlet' is the wordplay.
'not opening' means to remove the first letter (the opening letter is removed).
'outlet' becomes 'vent' (a vent is an outlet or opening).
'mad' with its first letter taken away is 'ad'.
'ad'+'vent'='ADVENT'
'in the run up' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for advent that I've seen before include "Period in the Christian calendar" , "The season leading up to Christmas" , "Coming (of Christmas)" , "when the Church year begins" , "introduction" .)