'capacidad' originates from Latin, specifically the word 'capacitās' (genitive 'capacitātis'), where the root 'capax' meant 'able' or 'spacious'.

'capacitās' from Classical Latin passed into Vulgar Latin and Old French as 'capacité', and from Romance (via Old Spanish influences) became the modern Spanish word 'capacidad'.

Initially it meant 'roominess' or 'the ability to hold (space)'; over time it broadened to include the sense of 'ability or competence' as well as physical 'capacity'.