Unity: 1 when a group of people or countries agree or are joined together: economic unity European unity 2 the quality of having matching parts: His essays often lack unity. 3 technical one of the three related principles that say a play should be about a single set of related events which take place in one place on one day. Solidarity: 1 loyalty and general agreement between all the people in a group, or between different groups because they all have a shared aim: a gesture of solidarity, an appeal for worker solidarity, 2 show/express/demonstrate your solidarity (with somebody): I came here to express my solidarity with you.