Second estate and Three estates

Second estate noun - The nobility in France and the peerage in Britain.

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

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