Main entry: dual
Definition: a grammatical number category referring to two items or units as opposed to one item (singular) or more than two items (plural)
Usage: ancient Greek had the dual form but it has merged with the plural form in modern Greek
Main entry: double, dual, duple
Definition: consisting of or involving two parts or components usually in pairs
Usage: an egg with a double yolk; a double (binary) star; double doors; dual controls for pilot and copilot; duple (or double) time consists of two (or a multiple of two) beats to a measure
Main entry: dual, double, treble, two-fold, twofold, three-fold, threefold
Definition: having more than one decidedly dissimilar aspects or qualities
Usage: a double (or dual) role for an actor; the office of a clergyman is twofold; public preaching and private influence- R.W.Emerson; every episode has its double and treble meaning-Frederick Harrison