for·ni·cate 
(fôrnĭ-kāt′)
(fôrnĭ-kāt′)intr.v. for·ni·cat·ed, for·ni·cat·ing, for·ni·cates
To commit fornication.
[Late Latin fornicārī, fornicāt-, from fornix, fornic-, vault, vaulted cellar, brothel; see gwher- in the Appendix of Indo-European roots.]
forni·ca′tor n.