Shared on line: season almost over (6)
I believe the answer is:
mutual
'shared' is the definition.
(similar in meaning)
'line season almost over' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'season' becomes 'autumn' (autumn is a season).
'almost' means to remove the last letter (most of the word but not all of it).
'over' says the letters should be written backwards.
'l'+'autumn'='lautumn'
'lautumn' with its last letter taken away is 'lautum'.
'lautum' backwards is 'MUTUAL'.
'on' is the link.
(Other definitions for mutual that I've seen before include "Felt by each towards the other, like friendship" , "given and received" , "Shared by two or more people" , "Affecting both parties" , "Held in common" .)