Regular on the day before the first of November (4)
I believe the answer is:
even
'regular' is the definition.
(I know that regular can be written as even)
'the day before the first of november' is the wordplay.
'the day' becomes 'eve' (eve is a kind of day).
'before' says to put letters next to each other.
'the first of november' becomes 'n' (est letter of 'november').
'eve'+'n'='EVEN'
'on' acts as a link.
(Other definitions for even that I've seen before include "Short joke" , "Like 2,4,6, ..." , "Smooth, uniform in quality" , "Regular - smooth" , "Yet; level" .)