dual vs duple

dual and duple both are adjectives.

Word	Noun	Adjective	Verb	Adverb
dual	No	Yes	No	No
duple	No	Yes	No	No

As adjectives, dual and duple are synonyms defined as:

dual and duple: consisting of or involving two parts or components usually in pairs

Other synonyms of dual include double.

dual (adjective)	duple (adjective)
consisting of or involving two parts or components usually in pairs	consisting of or involving two parts or components usually in pairs
a grammatical number category referring to two items or units as opposed to one item (singular) or more than two items (plural)
having more than one decidedly dissimilar aspects or qualities