Chennai vs Madras

Chennai and Madras both are nouns.

Word	Noun	Adjective	Verb	Adverb
Chennai	Yes	No	No	No
Madras	Yes	No	No	No

As nouns, Chennai and Madras are synonyms defined as:

Chennai and Madras: a city in Tamil Nadu on the Bay of Bengal; formerly Madras

Chennai (noun)	Madras (noun)
a city in Tamil Nadu on the Bay of Bengal; formerly Madras	a city in Tamil Nadu on the Bay of Bengal; formerly Madras
	a state in southeastern India on the Bay of Bengal (south of Andhra Pradesh); formerly Madras