crossing vs test-cross

crossing and test-cross both are nouns.

Word	Noun	Adjective	Verb	Adverb
crossing	Yes	No	No	No
test-cross	Yes	No	No	No

As nouns, test-cross is a hyponym of crossing; that is, test-cross is a word with a more specific, narrower meaning than crossing:

crossing: (genetics) the act of mixing different species or varieties of animals or plants and thus to produce hybrids
test-cross: a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring

Other hyponyms of crossing include dihybrid cross, monohybrid cross, reciprocal, reciprocal cross, testcross.

crossing (noun)	test-cross (noun)
a voyage across a body of water (usually across the Atlantic Ocean)	a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring
traveling across
(genetics) the act of mixing different species or varieties of animals or plants and thus to produce hybrids
a path (often marked) where something (as a street or railroad) can be crossed to get from one side to the other
a junction where one street or road crosses another
a point where two lines (paths or arcs etc.) intersect
a shallow area in a stream that can be forded