potter's earth vs potter's clay

potter's earth and potter's clay both are nouns.

Word	Noun	Adjective	Verb	Adverb
potter's earth	Yes	No	No	No
potter's clay	Yes	No	No	No

As nouns, potter's earth and potter's clay are synonyms defined as:

potter's earth and potter's clay: clay that does not contain any iron; used in making pottery or for modeling

potter's earth (noun)	potter's clay (noun)
clay that does not contain any iron; used in making pottery or for modeling	clay that does not contain any iron; used in making pottery or for modeling