Green’s Dictionary of Slang

(US) a public hanging.

1836		R. Weston Visit 96: The chief topic of discourse seemed to be the ‘hanging-bee’ at Trenton [DA].
1882		W.A. Baillie-Grohman Camps in the Rockies 350: The numerous hanging bees’ which cleared off the most desperate element in subsequent years had not yet been introduced.
1930		W. James Lone Cowboy 231: There’d been a ‘hanging bee’ [...] Cattle rustlers or horse thieves had had their horses led out from under ’em.
1941		E. Dick Vanguards of the Frontier (1965) 488: The theft of a horse meant a hanging-bee if the thief was caught.
1949		Monteleone Criminal Sl. (rev. edn) 112: hanging bee A lynching.