sexual_union has definitions from the fields of biology,sexuality
1
[ noun ] (biology,sexuality) the act of pairing a male and female for reproductive purposes

Examples

"the casual couplings of adolescents" "the mating of some species occurs only in the spring"

Used in print

(The Rev. John A. O'Brien, "Let's Take Birth Control...)

Denouncing the view that the sexual_union is an end in itself , the Conference declared : `` We steadfastly uphold what must always be regarded_as the governing considerations of Christian marriage .

*