Superfetation
Pronunciation : Su`per*fe*ta"tion
Part of Speech : n.
Etymology : [Cf. F. superf?tation.] (Physiol.)
Definition : Defn: The formation of a fetus at the result of an impregnation occurring after another impregnation but before the birth of the offspring produced by it. This is possible only when there is a double uterus, or where menstruation persists up to the time of the second impregnation. In then became a superfetation upon, and not an ingredient in, the national character. Coleridge.
Source : Webster's Unabridged Dictionary, 1913