Not always on the first of November (5)
I believe the answer is:
never
'not' is the definition.
(thesaurus)
'always on the first of november' is the wordplay.
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'on' says to put letters next to each other.
'the first of' indicates taking the first letters.
The first letter of 'november' is 'n'.
'ever' after 'n' is 'NEVER'.
(Other definitions for never that I've seen before include "Under no circumstances" , "Emphatic negative" , "Not ever" , "No way" , "At no time in the past or future" .)