1. favus — de Vaan
favus 'honeycomb' [m. o] (Varro+) Etymology unknown. One might follow WH and derive favus from PIE *bhuH- / *bhh2u- 'to dwell', in the sense that the honeycomb is (part of) the 'dwelling' of bees. Applying Vine's (2006) formulation of Thurneysen-Havet's Law, favus could then reflect a preform *bhouh2-o-, but final accentuation usually indicates an agent noun, whereas favus would rather require a resultative noun … — [de Vaan, s.v. favus, p. 221]