n. & v.
n. 1 a layer of dirt, froth, or impurities etc. forming at the top of liquid, esp. in boiling or fermentation. 2 (foll. by of) the most worthless part of something. 3 colloq. a worthless person or group.
v. (scummed, scumming) 1 tr. remove scum from; skim. 2 tr. be or form a scum on. 3 intr. (of a liquid) develop scum. scummy adj. (scummier, scummiest) adj.
[ ME f. MLG, MDu. schum, OHG scum f. Gmc ]