Thinker doesn't start in wet weather (4)
I believe the answer is:
rain
'wet weather' is the definition.
(rain is wet weather)
'thinker doesn't start' is the wordplay.
'thinker' becomes 'brain' (I've seen this in another clue).
'doesn't start' means to remove the first letter.
'brain' with its initial letter taken away is 'RAIN'.
'in' acts as a link.
(Other definitions for rain that I've seen before include "downfall?" , "Fall wetly" , "Storm" , "The right" , "Pelt" .)