O is an initial for 'omni'. It's the first letter in the word. The entire word is Latin for 'all'.
Omni tires are made by Omni United in Singapore. I have no reports of whether they are good or not.
Omni Superstore ended in 1997.
Omni Superstore was created in 1986.
The Omni Group was created in 1989.
Omni - magazine - was created in 1978.
Omni - magazine - ended in 1998.
Omni Coliseum was created in 1972.
Omni Coliseum ended in 1997.
Omni Aviation was created in 1988.
Omni-ID was created in 2007.
Dodge Omni was created in 1978.
The Omni Centre in Edinburgh was opened in 2002.