Definition - A language form that is used to refer to two things.

Example -
The words both, either, and twice are examples of English duals.

Etymology -
The term derives from the Latin dualis, which in turn derives from the Latin duo, two.

Oxford English Dictionary -
Its first citation in this sense is from 1607:
"In the holy tongue, the word which signifieth life is of the dual number."
(Bp. Andrewes Serm. II. 217)

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