'fiabilidad' originates from Spanish, specifically formed from the adjective 'fiable' plus the derivational suffix '-idad', where 'fiable' derives from Latin 'fidābilis' (from root 'fid-' meaning 'trust') and '-idad' comes from Latin '-itas' meaning 'state or quality'.

'fiable' changed from Latin 'fidābilis' through Old French 'fiable' and Medieval Spanish forms, and the noun form was created in Modern Spanish as 'fiabilidad' by adding the suffix '-idad'.

Initially it referred to being 'worthy of trust' (the quality of being trusted), and over time it evolved to denote the broader modern sense of 'the quality or degree of being reliable' (practical reliability, consistency, dependability).