'stable' (noun) originates from Latin, specifically the word 'stabulum', where 'stare' meant 'to stand' and 'stabulum' meant 'standing place' or 'stall'.

'stabulum' passed into Old French and/or Late Latin forms and into Middle English as 'stabel'/'stabel(e)', eventually yielding the modern English noun 'stable' and its plural 'stables'. The adjective 'stable' comes from Latin 'stabilis' (from 'stare') and entered English via Old French/Latin influence.

Initially it referred to a 'standing place' or 'stall'; over time it came to mean specifically a building for keeping animals (the noun) and, separately from 'stabilis', the adjective acquired the sense 'firm' or 'steadfast' in modern usage.