Holds back remainder over the wet season (9)
I believe the answer is:
restrains
'holds back' is the definition.
('restrain' can be a synonym of 'hold back')
'remainder over the wet season' is the wordplay.
'remainder' becomes 'rest' (synonyms).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'the wet season' becomes 'rains' (I've seen this in another clue).
'rest'+'rains'='RESTRAINS'
(Other definitions for restrains that I've seen before include "Sister ran (anag.)" , "Keeps back" , "Keeps under control or within limits" , "Keeps in check" .)