Support over month gets to proliferate (4)
I believe the answer is:
teem
'to proliferate' is the definition.
(I've seen this in another clue)
'support over month' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'month' becomes 'M' (standard abbreviation).
'tee'+'m'='TEEM'
'gets' is the link.
(Other definitions for teem that I've seen before include "Abound, swarm with" , "numerous" , "(Of rain) pour down" , "Bear" , "Come down hard" .)