Hephaestus vs Hephaistos

Hephaestus and Hephaistos both are nouns.

Word	Noun	Adjective	Verb	Adverb
Hephaestus	Yes	No	No	No
Hephaistos	Yes	No	No	No

As nouns, Hephaestus and Hephaistos are synonyms defined as:

Hephaestus and Hephaistos: (Greek mythology) the lame god of fire and metalworking in ancient mythology; identified with Roman Vulcan

Hephaestus (noun)	Hephaistos (noun)
(Greek mythology) the lame god of fire and metalworking in ancient mythology; identified with Roman Vulcan	(Greek mythology) the lame god of fire and metalworking in ancient mythology; identified with Roman Vulcan