'inquietud' originates from Spanish, ultimately from Latin 'inquietudo' (or 'inquietus'), where 'in-' meant 'not' and 'quietus' meant 'at rest' or 'calm'.

'inquietud' changed from Latin 'inquietudo' into Old Spanish forms (e.g. medieval Spanish 'inquietud') and eventually became the modern Spanish word 'inquietud'.

Initially it meant 'absence of quiet or rest' and over time it came to denote both physical/mental restlessness and anxious concern; the core idea of lack of calm has been retained.