Couple or duo (4)
I believe the answer is:
pair
I believe this is a double definition.
'couple' is the first definition.
(synonyms)
'duo' is the second definition.
(synonyms)
(Other definitions for pair that I've seen before include "Twosome" , "Two of a kind, as in cards" , "item" , "Twins" , "players of duet?" .)