There are several synonyms for the word "Ooecium" which is basically a sac or structure where eggs are laid, hatched, and protected. Other terms that can be used synonymously with "ooecium" include "brood pouch," "ovisac" or "ovary pouch." These words are often used in scientific and medical contexts to describe reproductive structures, such as in studies of marine life or parasitic organisms. However, it's worth noting that these terms are not interchangeable with "ooecium" in all cases, and their precise usage may depend on the specific context in which they are being used.