Thessalonica vs Thessaloniki

Thessalonica and Thessaloniki both are nouns.

Word	Noun	Adjective	Verb	Adverb
Thessalonica	Yes	No	No	No
Thessaloniki	Yes	No	No	No

As nouns, Thessalonica and Thessaloniki are synonyms defined as:

Thessalonica and Thessaloniki: a port city in northeastern Greece on an inlet of the Aegean Sea; second largest city of Greece

Other synonyms of Thessalonica include Salonica, Salonika.

Thessalonica (noun)	Thessaloniki (noun)
a port city in northeastern Greece on an inlet of the Aegean Sea; second largest city of Greece	a port city in northeastern Greece on an inlet of the Aegean Sea; second largest city of Greece