O.E.
triewð (W.Saxon),
treowð (Mercian) "faithfulness, quality of being true," from
triewe, treowe "faithful" (see
true). Meaning "accuracy, correctness" is from 1570. Unlike
lie (v.), there is no primary verb in Eng. for "speak the truth." Noun sense of "something that is true" is first recorded c.1362.
"Let [Truth] and Falsehood grapple; who ever knew Truth put to the worse, in a free and open encounter." [Milton, "Areopagitica," 1644]
Truth squad in U.S. political sense first attested 1952.
Truthiness "act or quality of preferring concepts or facts one wishes to be true, rather than those known to be true," catch word popularized in this sense by U.S. comedian Stephen Colbert, declared by American Dialect Society to be "2005 Word of the Year."