Dual

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late Middle English (as a noun denoting either of the two middle incisor teeth in each jaw): from Latin dualis, from duo ‘two’.

wiktionary

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Borrowed from Latin dualis(“two”), from duo(“two”) + adjective suffix -alis

etymonline

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dual (adj.)

c. 1600, in grammar, "the form or number relating to two," from Latin dualis "that contains two; the dual number, duality," from duo "two" (from PIE root *dwo- "two"). General sense of "relating to two, expressing two, composed or consisting of two parts" is from 1650s. Related: Dually.