potty chair vs potty seat

potty chair and potty seat both are nouns.

Word	Noun	Adjective	Verb	Adverb
potty chair	Yes	No	No	No
potty seat	Yes	No	No	No

As nouns, potty chair and potty seat are synonyms defined as:

potty chair and potty seat: toilet consisting of a small seat used by young children

potty chair (noun)	potty seat (noun)
toilet consisting of a small seat used by young children	toilet consisting of a small seat used by young children