first estate vs Lords Spiritual

first estate and Lords Spiritual both are nouns.

Word	Noun	Adjective	Verb	Adverb
first estate	Yes	No	No	No
Lords Spiritual	Yes	No	No	No

As nouns, first estate and Lords Spiritual are synonyms defined as:

first estate and Lords Spiritual: the clergy in France and the heads of the church in Britain

first estate (noun)	Lords Spiritual (noun)
the clergy in France and the heads of the church in Britain	the clergy in France and the heads of the church in Britain