1712, "form, shape" (earlier plasm, 1620), from L.L. plasma, from Gk. plasma "something molded or created," from plassein "to mold," originally "to spread thin," from PIE *plath-yein, from base *pele- "flat, to spread" (see plane (1)). Sense of "liquid part of blood" is from 1845; that of "ionized gas" is 1928.