Third estate and Three estates

Third estate noun - The common people.

Three estates and third estate are semantically related. In some cases you can use "Three estates" instead a noun phrase "Third estate".

Three estates noun - A major social class or order of persons regarded collectively as part of the body politic of the country (especially in the United Kingdom) and formerly possessing distinct political rights.

Third estate and three estates are semantically related. Sometimes you can replace phrase "Third estate" with "Three estates", this phrases are similar.