Weather provided by sun god in autumn (8)
I believe the answer is:
rainfall
'weather' is the definition.
(rainfall is a kind of weather)
'by sun god in autumn' is the wordplay.
'by' says to put letters next to each other.
'sun god' becomes 'ra'.
'autumn' becomes 'fall' ('fall' can be a synonym of 'autumn').
'ra'+'in' is 'rain'.
'rain'+'fall'='RAINFALL'
'provided' acts as a link.
(Other definitions for rainfall that I've seen before include "Water falling in drops" , "Precipitation, get out umbrella" , "Climate measure" , "Form of precipitation" , "Amount of water coming down" .)