'defoamer' originates from English, specifically formed from the prefix 'de-' (from Latin 'de-', meaning 'remove' or 'reduce') + the noun 'foam' + the agent-forming suffix '-er'.

'foam' goes back to Old English (e.g. 'fām' or 'fōm') meaning 'froth'; the productive English prefix 'de-' (from Latin) combined with 'foam' to form the verb 'defoam' in modern technical English, and the agent noun 'defoamer' developed thereafter in the 19th–20th century industrial and chemical contexts.

Initially it literally meant 'one that removes foam'; over time the term has remained stable but broadened in technical usage to cover a range of chemical antifoams and mechanical devices used across industries.