dual

consisting of or involving two parts or components usually in pairs

an egg with a double yolk

having more than one decidedly dissimilar aspects or qualities; ;, R.W.Emerson; -Frederick Harrison

a double (or dual) role for an actor

a grammatical number category referring to two items or units as opposed to one item (singular) or more than two items (plural)

ancient Greek had the dual form but it has merged with the plural form in modern Greek