Oogonium

Oogonium: A female ancestral germ cell that divides several times to give rise to an oocyte that, in turn, develops into an ovum (an egg).

The second "o" in oogonium is pronounced separately from the first: o·o·gon·i·um. The word was created from the prefix "oo-" (Greek oon, egg) + "gonium" (New Latin for cell) = the egg cell.