[intransitive, transitive] if two or more substances mix or you mix them, they combine, usually in a way that means they cannot easily be separated Oil and water do not mix. mix with something Oil does not mix with water. mix A and B (together) Mix all the ingredients together in a bowl. If you mix blue and yellow, you get green. mix A with B I don't like to mix business with pleasure (= combine social events with doing business).