1. The action of coupling or linking two things together, or condition of being coupled; connexion, union. Obs.
1752 Johnson Rambler No. 194 310 Wit+is the unexpected copulation of ideas. 1752 H. Walpole Corr. (1837) I. 179 A pyramid which by a most unnatural copulaton is at once a grotto and a greenhouse.

b. Grammatical or logical connexion.

c. quasi-concr. A combination. Obs. rare.
1774 H. Walpole Let. Sir W. Hamilton 19 June, A new instrument+a copulation of a harpsicord and a violin.

2. spec. The union of the sexes in the act of generation. (Now chiefly a term of Zoology.)

[OED]