What is the meaning of Oni?

A Japanese evil spirit or demon.

they (third person personal masculine animate plural)

nominative animate masculine plural of onen

yes

water

noise

they (masculine plural)

nominative masculine plural of onen

they (masculine plural, more than two)

honey

honey bee, Apis mellifera

stingless bee

one

they (some people, people in general)

Rōmaji transcription of おに

they (third-person masculine personal nominative)

they (nominative plural of ȏn (he))

masculine animate nominative plural of on (they)

accusative singular of on

unless

until

used to introduce a negative question

used to form a tag question

today

Source: wiktionary.org