Turn up suitable bucket (4)
I believe the answer is:
teem
'bucket' is the definition.
(both can mean to rain)
'turn up suitable' is the wordplay.
'turn up' is a reversal indicator.
'suitable' becomes 'meet' (synonyms).
'meet' written backwards gives 'TEEM'.
(Other definitions for teem that I've seen before include "Swarm around meet" , "Bucket down" , "Come down hard" , "Abound, swarm with" , "Be full" .)