conjugation vs sexual union

conjugation and sexual union both are nouns.

Word	Noun	Adjective	Verb	Adverb
conjugation	Yes	No	No	No
sexual union	Yes	No	No	No

As nouns, conjugation and sexual union are synonyms defined as:

conjugation and sexual union: the act of pairing a male and female for reproductive purposes

Other synonyms of conjugation include coupling, mating, pairing, union.

conjugation (noun)	sexual union (noun)
the act of pairing a male and female for reproductive purposes	the act of pairing a male and female for reproductive purposes
the act of making or becoming a single unit
a class of verbs having the same inflectional forms
the complete set of inflected forms of a verb
the inflection of verbs
the state of being joined together