betbet

The story

From 16th-century criminal slang, perhaps from Middle English bet (‘something better, advantage, luck’), from Old English bet, bett (“better”, adverb); or, alternatively from abet, from Middle English abet, abette, from Old French abet (‘incitement to evil’), from Old French abeter (‘to entice’), from a- (‘to’) + beter (‘hound on, urge, to bait’); ultimately from Proto-West Germanic *baitijan (‘to bait, entice’), related to Old English bǣtan (‘to bait’).1disputed Scholars disagree here; the competing view is quoted as the source gives it.

Full etymology on Wiktionary