This name had its origin in some feat of personal strength or courage. There is the following tradition of its origin: A strong man of the name of Ruel, having turned a wild bull by the head, which violently ran against King Robert Bruce in Stirling Park, received from the king the lands of Bedrule, and the name of Turnbull.

Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.

TURNBULL. Probably local. A tradition has, however, been made to fit the name. It seems that king Robert Bruce, being once upon a time in Stirling park, was attacked by a ferocious bull. A brave fellow, called Ruel, came to the rescue; turned tlie hull; and got not only the king's thanks, but the lands of Bedrule, and a new surname. It appears certain, however, that a champion of great stature called Turnbull fouglit under king David Bruce, at the battle of Halidon, and was killed there. Nisbet's Heraldry. Tlie analogous name Chacelyon is found in Essex, temp. Hen. VI. Knatchbull may also belong to this class.

Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.