What is the meaning of ön-?

self-

proto-

pre-, before

Marks a negated transitive verb with a third-person object/patient, forming a negative circumfix with -'da.

Marks a transitive verb in admonitive mood with a third-person object/patient, forming an admonitive circumfix with -'no.

Marks a transitive verb in prohibitive mood with a third-person object/patient or with a first-person object/patient and second-person subject/agent, forming a prohibitive circumfix with -i.

Optionally marks a transitive verb in imperative, jussive, or rogative mood to lend it a sociative meaning, indicating an action to be performed with others at the speaker’s request, and forming a circumfix with -kö, -iye, or -'ñojo respectively.

Source: wiktionary.org