- abet (v.)

- late 14c., "urge on, incite" (implied in abetting), from Old French abeter "to bait, to harass with dogs," literally "to cause to bite," from a- "to" (see ad-) + beter "to bait." This verb is probably from Frankish or some other Germanic source (perhaps Low Franconian betan "incite," or Old Norse beita "cause to bite"); ultimately from Proto-Germanic *baitjan, from PIE root *bheid- "to split" (see fissure (n.)). Sense of "encourage by aid or approval" is from 1779. Related: Abetted; abetting.
- bet

- 1590s, as both a verb and noun, in the argot of petty criminals, of unknown origin; probably a shortening of abet or else from obsolete beet "to make good," from Old English bætan "make better, arouse, stimulate," from Proto-Germanic *baitjan, in which case the verb would be the original. The original notion is perhaps "to improve" a contest by wagering on it, or it is from the "bait" sense in abet. Used since 1852 in various American English slang assertions (compare you bet "be assured," 1857). Related: Betting.