clear top layer of liquid
Refers to the clear liquid that rises to the top of soup, broth, or similar mixtures. Rare term; 上澄み (うわずみ) is the common modern equivalent.
See also: 上澄み
someone else's share; skimmed profit
Idiomatic use, almost exclusively in the set phrase 上汁を吸う (to take a cut or profit from someone else's work). Rare and old-fashioned.
See also: 上汁を吸う
I scooped up and drank the clear liquid on top of the miso soup.
He is skimming a profit as a middleman.
Compound of 上 (うわ, 'top') and 汁 (しる, 'liquid, juice'). The idiomatic sense likely derives from the image of skimming the best part off the top.