Stratum and Three estates

Stratum noun - One of the segments of society into which people are grouped.

Three estates and stratum are semantically related. In some cases you can replace phrase "Three estates" with "Stratum", this terms are similar.

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.

Stratum and three estates are semantically related. You can use "Stratum" instead a noun phrase "Three estates".