What is "superfetate"

Superfetate \Su`per*fe"tate\, v. i. [L. superfetare; super above, over + fetare to bring forth.] To conceive after a prior conception, but before the birth of the offspring.

The female . . . is said to superfetate.
--Grew.

vb. To conceive after a prior conception, but before the birth of the offspring.

v. conceive when a fetus is already present in the uterus