se·ro·sa 
(s
ĭ-r
ōs
ə, -z
ə)
n. pl. se·ro·sas or
se·ro·sae (-s
ē, -z
ē)
1. A serous membrane, especially one that lines the pericardial, pleural, and peritoneal cavities, enclosing their contents.
2. A membrane that surrounds the embryo of birds, reptiles, and many insects.
[New Latin serōsa, feminine of serōsus, serous, from Latin serum, serum.]
se·rosal (-zəl) adj.