Serum

From Latin serum ("whey"). Cognates: French sÃ©rum, Spanish suero, Italian siere, siero.

Full definition of serum

(plural serums or sera)

The clear yellowish fluid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot. Also called blood serum.
Blood serum from the tissues of immunized animals, containing antibodies and used to transfer immunity to another individual, called antiserum.
A watery fluid from animal tissue, especially one that moistens the surface of serous membranes or that is exuded by such membranes when they become inflamed, such as in edema or a blister.
The watery portion of certain animal fluids, as blood, milk, etc; whey.
(skincare) An intensive moisturising product to be applied after cleansing but before a general moisturiser.