onto-
word-forming element meaning “a being, individual; being, existence,” from stem of Greek on (genitive ontos) “being,” neuter present participle of einai “to be” (from PIE root *es- “to be”). (etymonline.com)
So onto- can refer to an individual being or being in general. Translation shows us that being itself is one, therefore indivisible, therefore the only individual.
–Mike Zonta, H.W., M., BB editor