two vs dyad

two and dyad both are nouns.

Word	Noun	Adjective	Verb	Adverb
two	Yes	Yes	No	No
dyad	Yes	No	No	No

As nouns, dyad is a hyponym of two; that is, dyad is a word with a more specific, narrower meaning than two:

two: the cardinal number that is the sum of one and one or a numeral representing this number
dyad: two items of the same kind

Other hyponyms of two include craps, snake eyes, brace, couple, couplet, distich, duad, duet, duo, pair, span, twain, twosome, yoke.

two (noun)	dyad (noun)
one of the four playing cards in a deck that have two spots	two items of the same kind
the cardinal number that is the sum of one and one or a numeral representing this number

two (adjective)	dyad (adjective)
being one more than one