It's an English name, although the nationality of people with that name is American. It may be derived from a distant Spanish or other Romance language origin -- or it could just be a corruption of something more recognizably English. The web sites that suggest an American Indian origin of the surname are mainly just guessing without having looked at the document record (censuses, land and marriage records, etc.) The other answer that it's "actually Spanish and Irish" is in the ballpark. The Omohundro family was settled in the British Colony of Virginia by the middle to late 1600s. Virtually everyone alive today with the surname Omohundro or Mohundro traces back to the same colonial American from Westmoreland County, Virginia.
It's actually spanish and Irish
Most of the sources suggest that the nationality of the surname Omohundro is American Indian. The history shows that the surname was recorded in Westmoreland Co. VA. On 30 December 1670 by Richard Omohundro.