peneplane vs peneplain

peneplane and peneplain both are nouns.

Word	Noun	Adjective	Verb	Adverb
peneplane	Yes	No	No	No
peneplain	Yes	No	No	No

As nouns, peneplane and peneplain are synonyms defined as:

peneplane and peneplain: a more or less level land surface representing an advanced stage of erosion undisturbed by crustal movements

peneplane (noun)	peneplain (noun)
a more or less level land surface representing an advanced stage of erosion undisturbed by crustal movements	a more or less level land surface representing an advanced stage of erosion undisturbed by crustal movements