trisomy vs trisomy 21

trisomy and trisomy 21 both are nouns.

Word	Noun	Adjective	Verb	Adverb
trisomy	Yes	No	No	No
trisomy 21	Yes	No	No	No

As nouns, trisomy 21 is a hyponym of trisomy; that is, trisomy 21 is a word with a more specific, narrower meaning than trisomy:

trisomy: chrosomal abnormality in which there is one more than the normal number of chromosomes in a cell
trisomy 21: a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation

Other hyponyms of trisomy include Down's syndrome, Down syndrome, mongolianism, mongolism.

trisomy (noun)	trisomy 21 (noun)
chrosomal abnormality in which there is one more than the normal number of chromosomes in a cell	a congenital disorder caused by having an extra 21st chromosome; results in a flat face and short stature and mental retardation