dual vs twofold

dual and twofold both are adjectives.

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

As adjectives, dual and twofold are synonyms defined as:

dual and twofold: having more than one decidedly dissimilar aspects or qualities

Other synonyms of dual include double, three-fold, threefold, treble, two-fold.

dual (adjective)	twofold (adjective)
consisting of or involving two parts or components usually in pairs	twice as great or many
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
having more than one decidedly dissimilar aspects or qualities

dual (adverb)	twofold (adverb)
	by a factor of two