Sri Lankan vs Ceylonese

Sri Lankan is a noun but Ceylonese is not a noun.

Word	Noun	Adjective	Verb	Adverb
Sri Lankan	Yes	Yes	No	No
Ceylonese	No	Yes	No	No

As adjectives, Sri Lankan and Ceylonese are synonyms defined as:

Sri Lankan and Ceylonese: of or relating to Sri Lanka (formerly Ceylon) or its people or culture

Sri Lankan (noun)	Ceylonese (noun)
a native or inhabitant of Sri Lanka

Sri Lankan (adjective)	Ceylonese (adjective)
of or relating to Sri Lanka (formerly Ceylon) or its people or culture	of or relating to Sri Lanka (formerly Ceylon) or its people or culture