__ opener (6)
(Other definitions for season that I've seen before include "make things palatable" , "Time of 9" , "Quarter of the year" , "Add flavouring" , "eg.Summer" .)
'opener' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for intro that I've seen before include "Opening bars of a song" , "starter" , "First notes" , "Preamble" , "Jazz piece" .)