These are some of the English words that begin with the letters OMNI...

Omnibus, Omnify, Omnivore, Omnipotent, Omnipresent

As you can see, this beginning isn't particularly common, and most of the words that use it don't appear very frequently. It often relates to the concept of "all" or "everything"; someone omnipotent is all-powerful, something omnipresent is everywhere, and an omnivore eats both plants and meat.

Some brand or model names also start with OMNI. For example, Chrysler used to make a compact car called the Dodge Omni; it was quite similar to the Plymouth Horizon.