'vaciar' originates from Latin, specifically the verb 'vacuare', where 'vacuus' meant 'empty'.

'vaciar' changed from the Latin verb 'vacuare' (through Vulgar Latin *vaciare) into Old Spanish forms such as 'vaciar' and eventually became the modern Spanish 'vaciar'.

Initially it meant 'to make empty' or 'to render empty' in a literal sense; over time it retained that meaning and additionally developed reflexive uses meaning 'to become empty' and figurative senses like 'to empty oneself of feelings'.