Tbilisi vs Tiflis

Tbilisi and Tiflis both are nouns.

Word	Noun	Adjective	Verb	Adverb
Tbilisi	Yes	No	No	No
Tiflis	Yes	No	No	No

As nouns, Tbilisi and Tiflis are synonyms defined as:

Tbilisi and Tiflis: the capital and largest city of Georgia on the Kura river

Other synonyms of Tbilisi include capital of Georgia.

Tbilisi (noun)	Tiflis (noun)
the capital and largest city of Georgia on the Kura river	the capital and largest city of Georgia on the Kura river