From the Dictionary of English & Welsh Surnames: "Turnbull, Trumble, Trumbull -? Nickname 'turnbull' (?) There can be little doubt about the origin of this name. Two great clan nicknames grew up in Liddesdale and the 'Debatable Land' the Armstrongs and the Turnbulls, both significant of that prowess which was so necessary in the time of Scotch and English raids across the border. To turn the bull at the baiting would be and exploit worthy a sobriquet in those rude times, and the possessor would be proud to bear it. The idea that the name is local must be given up. Trumble is a corruption of Turnbull not Turnbull of Trumble. The earliest form is Turnebull."