Shiva vs Siva

Shiva and Siva both are nouns.

Word	Noun	Adjective	Verb	Adverb
Shiva	Yes	No	No	No
Siva	Yes	No	No	No

As nouns, Shiva and Siva are synonyms defined as:

Shiva and Siva: the auspicious one; a major divinity in the later Hindu pantheon

Shiva (noun)	Siva (noun)
the auspicious one; a major divinity in the later Hindu pantheon	the auspicious one; a major divinity in the later Hindu pantheon