"place in a stable for animals," Old English steall "place where cattle are kept, place, position," from Proto-Germanic *stallaz (cf. Old Norse stallr "pedestal for idols, altar," Old Frisian stal, Old High German stall "stand, place, stable, stall," German Stall "stable," Stelle "place"), earlier *stalnaz- or *stathlo-, from PIE root *stel- "to put, stand," with derivatives referring to a standing object or place (cf. Greek stele "standing block, slab," Latin stolidus "insensible, dull, brutish," properly "unmovable").
The word passed into Romanic languages (cf. Italian stallo "place," stalla "stable;" Old French estal "place, position, stand, stall," French étal "butcher's stall"). Several meanings, including that of "a stand for selling" (mid-13c., implied in stallage "tax levied for the privilege of erecting a stall at a market or fair"), are from (or influenced by) Old French estal. Meaning "partially enclosed seat in a choir" is attested from c.1400; that of "urinal in a men's room" is from 1967.