dual

adjective

1. of, relating to, or noting two.
2. composed or consisting of two people, items, parts, etc., together; twofold; double: dual ownership; dual controls on a plane.
3. having a twofold, or double, character or nature.
4. Grammar. being or pertaining to a member of the category of number, as in Old English, Old Russian, or Arabic, that denotes two of the things in question.

noun Grammar.

5. the dual number.
6. a form in the dual, as Old English git “you two,” as contrasted with ge “you” referring to three or more.

adjective

1. relating to or denoting two
2. twofold; double
3. (in the grammar of Old English, Ancient Greek, and certain other languages) denoting a form of a word indicating that exactly two referents are being referred to
4. maths logic (of structures or expressions) having the property that the interchange of certain pairs of terms, and usually the distribution of negation, yields equivalent structures or expressions

noun

5. grammar
   1. the dual number
   2. a dual form of a word

verb duals, dualling or dualled

6. (tr) British to make (a road) into a dual carriageway