According to "Patronymica Britannica: A Dictionary of the Family Names of the United Kingdom" (p. 345) by Mark Antony Lower (published in London, England in 1860 by John Russell Smith of 36 Soho Square), "thwaite" is a Saxon word whose meaning is somewhat disputed, but which is generally understood to mean an area that has been cleared of forest. Surnames ending in this word originated in northwestern England, specifically in the counties of Cumberland, Westmoreland and North Lancashire. There is a village named Thackthwaite in the old county of Cumberland, which borders Scotland. The ancient county became part of Cumbria in 1974. It is reasonable to suppose that families with the surname THACKTHWAITE originated in the general region of that village or at least in old Cumberland County.