twofold vs dual

twofold and dual both are adjectives.

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

As adjectives, twofold and dual are synonyms defined as:

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

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

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

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