'sentimiento' originates from Latin, specifically the Late Latin word 'sentimentum', where the verb 'sentire' meant 'to feel'.

'sentimentum' in Late Latin passed into Old Spanish as 'sentimiento' (via Romance developments) and eventually became the modern Spanish noun 'sentimiento'.

Initially it meant 'the act or faculty of sensing/feeling', but over time it evolved into the modern sense of 'emotion, feeling, or opinion'.