Late 19th century; earliest use found in Chicago Clinic. Alteration of supernatant, after words in -ate. As noun perhaps formed independently, after words in -ate.
supernate2
/suːpəˈneɪt//sjuːpəˈneɪt/
Chemistry and Biologyrare
verb
[with object]And without object. Of a liquid: to lie above and in contact with (a solid residue, other liquid, etc.).
Origin
Late 17th century; earliest use found in William Salmon (1644–1713), medical empiric and author. From classical Latin supernatāre to swim over or above, to lie on the surface of a liquid, to float on top, (of liquids) to flow freely on top.