Twosome, couple (4)
I believe the answer is:
pair
This clue is a double definition.
'twosome' is the first definition.
(I know that twosome can be written as pair)
'couple' is the second definition.
(I know that couple can be written as pair)
(Other definitions for pair that I've seen before include "players of duet?" , "Agreement to avoid division" , "Brace, couple" , "Duo" , "Husband and wife" .)