treason (n.) Look up treason at Dictionary.com
c. 1200, "betraying; betrayal of trust; breach of faith," from Anglo-French treson, from Old French traison "treason, treachery" (11c.; Modern French trahison), from Latin traditionem (nominative traditio) "a handing over, delivery, surrender" (see tradition, which is its doublet). The Old French form was influenced by the verb trair "betray."
Vpon Thursday it was treason to cry God saue king James king of England, and vppon Friday hye treason not to cry so. [Thomas Dekker, "The Wonderfull Yeare 1603"]
In old English law, high treason is violation by a subject of his allegiance to his sovereign or to the state; distinguished from petit treason, treason against a subject, such as murder of a master by his servant. Constructive treason was a judicial fiction whereby actions carried out without treasonable intent, but found to have the effect of treason, were punished as though they were treason itself. The protection against this accounts for the careful wording of the definition of treason in the U.S. Constitution.