retrocopulation
/ˌrɛtrə(ʊ)ˌkɒpjʊˈleɪʃn/Chiefly Zoology rare
noun
The action or fact of copulating back to back (as is a normal stage of mating in dogs, and was formerly supposed to occur in retromingent mammals). Later also: the action of copulating from behind (i.e. with the male behind the female, as in most mammals).
Origin
Mid 17th century; earliest use found in Thomas Browne (1605–1682), physician and author. From retro- + copulation.