Must nothing cancel the first of November? (5)
I believe the answer is:
ought
'must' is the definition.
(synonyms)
'nothing cancel the first of november?' is the wordplay.
'nothing' becomes 'nought' (synonyms).
'cancel' suggests deleting specific letters.
'the first of november?' becomes 'n' (1st letter of 'november').
'nought' with 'n' taken away is 'OUGHT'.
(Other definitions for ought that I've seen before include "Strange thing" , "outdated anything at all?" , "It expresses duty or obligation" , "Should, had, better" , "Has a duty (to do something)" .)