The Collaborative International Dictionary of English v.0.48:

Oogonium \O`o*go"ni*um\, n.; pl. L. Oogonia, E. Oogoniums.
   [NL., fr. Gr. w,'o`n an egg + ? offspring.] (Bot.)
   A special cell in certain cryptogamous plants containing
   oospheres, as in the rockweeds (Fucus), and the orders
   Vaucherieae and Peronosporeae.
   [1913 Webster]