Green’s Dictionary of Slang

(US) hot, illicit whisky.

1934		J.H. O’Hara Appointment in Samarra (1935) 83: Boilo is hot moonshine, and Ed did not approve of it.
2001		baaabby’s LiveJournal 23 Dec. 🌐 I’ve been looking for this recipe, for something called Boilo, or Broilo, or Boillo for like 2 hours now!! [...] It’s an alcoholic drink...like a spiced rum...
2001		CoalRegion.com 🌐 Boilo – Traditional Yuletide drink of the Coal Region [...] Boilo is traditionally made during the Christmas and New Year’s holiday. It’s great on those cold winter nights. Beware, this can knock you for a loop! Cheers!