Lao-tzu vs Laozi

Lao-tzu and Laozi both are nouns.

Word	Noun	Adjective	Verb	Adverb
Lao-tzu	Yes	No	No	No
Laozi	Yes	No	No	No

As nouns, Lao-tzu and Laozi are synonyms defined as:

Lao-tzu and Laozi: Chinese philosopher regarded as the founder of Taoism (6th century BC)

Other synonyms of Lao-tzu include Lao-tse, Lao-zi.

Lao-tzu (noun)	Laozi (noun)
Chinese philosopher regarded as the founder of Taoism (6th century BC)	Chinese philosopher regarded as the founder of Taoism (6th century BC)