ETYM French malcontent.
A person who is discontented or disgusted.
A discontented person: one who bears a grudge from a sense of grievance or thwarted ambition; one who is in active opposition to an established order or government; rebel.

ETYM Of Scand. origin; cf. Dan. and Swed. skum, Icel. skűm, lg. schum, Dutch schuim, Old High Germ. scűm, German schaum; probably from a root meaning, to cover. Related to Hide skin, Meerschaum, Skim, Sky.
A film of impurities or vegetation that can form on the surface of a liquid.