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.
Dodge Omni was created in 1978.
Omni - magazine - was created in 1978.
Omni - magazine - ended in 1998.
The Omni Group was created in 1989.
Omni Aviation was created in 1988.
Omni Coliseum was created in 1972.
Omni Coliseum ended in 1997.
Omni Superstore ended in 1997.
Omni Superstore was created in 1986.
Omni-ID was created in 2007.
The Omni Centre in Edinburgh was opened in 2002.