The correct antonym of the word 'DEITY' is: Demon.

Deity: Refers to a god or a goddess, a divine being with supernatural powers and often worshipped or revered. Therefore, "demon" directly opposes the positive and divine nature associated with a deity, making it the most accurate antonym in this context.

• Providence: Can have religious connotations but in general implies divine guidance or fate, not necessarily opposing the concept of a deity.
• Eternity: Refers to timelessness or endless duration, not related to the existence or non-existence of deities.
• Omnipresent: Describes being present everywhere at all times, not an opposite characteristic of being a deity.