SERUM

I. noun (plural ~s or sera) Etymology: Latin, whey, wheylike fluid; akin to Greek oros whey Date: 1665 the watery portion of an animal fluid remaining after coagulation:, a. blood ~ , anti~ , whey , a normal or pathological serous fluid (as in a blister), the watery part of a plant fluid, II. adjective Date: 1876 occurring or found in the blood ~