otherwise; if not; or (else)

One can't go beyond one's limits with exercising and stay within the bounds of what one can do. Otherwise, it can have negative effects on the body.

Don't speak unless you have something worth saying.

Otherwise, it is considered impolite to pass food with the left hand, because the left hand is used for bathing.

I will not believe it unless and until he tells me so.

One must have conviction in law, or its existence will be superficial only.