Diviner month, you said, before year's end (5)
I believe the answer is:
augur
'diviner' is the definition.
(augur is a kind of diviner)
'month you said before year's end' is the wordplay.
'month' becomes 'Aug' (abbreviation for August).
'you said' becomes 'U' (homophone of 'you').
'before' says to put letters next to each other.
'end' suggests the final letters.
The final letter of 'year' is 'r'.
'aug'+'u'+'r'='AUGUR'
(Other definitions for augur that I've seen before include "Predict as from omens" , "Harbinger" , "Foreshadow" , "Portend, foretell" , "Prognosticate" .)