three vs threesome

three and threesome both are nouns.

Word	Noun	Adjective	Verb	Adverb
three	Yes	Yes	No	No
threesome	Yes	No	No	No

As nouns, three and threesome are synonyms defined as:

three and threesome: the cardinal number that is the sum of one and one and one

Other synonyms of three include 3, deuce-ace, III, leash, tercet, ternary, ternion, terzetto, tierce, trey, triad, trine, trinity, trio, triplet, troika.

three (noun)	threesome (noun)
one of four playing cards in a deck having three pips	three people considered as a unit
the cardinal number that is the sum of one and one and one	the cardinal number that is the sum of one and one and one

three (adjective)	threesome (adjective)
being one more than two