salt plain vs salt flat

salt plain and salt flat both are nouns.

Word	Noun	Adjective	Verb	Adverb
salt plain	Yes	No	No	No
salt flat	Yes	No	No	No

As nouns, salt plain and salt flat are synonyms defined as:

salt plain and salt flat: a flat expanse of salt left by the evaporation of a body of salt water

salt plain (noun)	salt flat (noun)
a flat expanse of salt left by the evaporation of a body of salt water	a flat expanse of salt left by the evaporation of a body of salt water