XY vs sex chromosome

XY and sex chromosome both are nouns.

Word	Noun	Adjective	Verb	Adverb
XY	Yes	No	No	No
sex chromosome	Yes	No	No	No

As nouns, sex chromosome is a hypernym of XY; that is, sex chromosome is a word with a broader meaning than XY:

XY: (genetics) normal complement of sex hormones in a male
sex chromosome: (genetics) a chromosome that determines the sex of an individual

XY (noun)	sex chromosome (noun)
(genetics) normal complement of sex hormones in a male	(genetics) a chromosome that determines the sex of an individual