reciprocal cross vs crossing

reciprocal cross and crossing both are nouns.

Word	Noun	Adjective	Verb	Adverb
reciprocal cross	Yes	No	No	No
crossing	Yes	No	No	No

As nouns, crossing is a hypernym of reciprocal cross; that is, crossing is a word with a broader meaning than reciprocal cross:

reciprocal cross: hybridization involving a pair of crosses that reverse the sexes associated with each genotype
crossing: (genetics) the act of mixing different species or varieties of animals or plants and thus to produce hybrids

Other hypernyms of reciprocal cross include cross, crossbreeding, hybridisation, hybridization, hybridizing, interbreeding.

reciprocal cross (noun)	crossing (noun)
hybridization involving a pair of crosses that reverse the sexes associated with each genotype	a voyage across a body of water (usually across the Atlantic Ocean)
	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