schummeln

Etymology
There are two main theories, which need not be mutually exclusive but may complement each other.
 * From dialectal, originally probably “to move back and forth”, whence various attested senses: “waver, totter; rock, swing, push; chase off; abscond, steal away; take clandestinely; rummage; bustle about; do housework”, etc. In favour of this derivation speaks that the sense “to cheat” was sometimes associated with “trickery through swift movements”, especially in the context of gambling. The verb (in the above-mentioned senses) is found in dialects as far south as , but  considered it chiefly Low German and the earliest attestations are of late  (1410: “to do kitchenwork”, 1530: “to rock, move back and forth”); hence probably of northern origin through , eventually perhaps onomatopoeic. Compare modern 🇨🇬. Compare also , from.
 * Through a dialectally attested sense “to trade (of a Jewish merchant)”, from, an acronym for the cities of , , , the so-called Schum cities, old centres of Jewish religion and trade. However, a verb derived from this acronym is not attested in Yiddish and the sense “to trade” may be derived from the sense “to cheat”, rather than vice versa.

Verb

 * 1)  to cheat especially in games, but also in business, school, etc.