Word Origin & History
c.1300, "absolute ruler," from O.Fr. tyrant (12c.), from L. tyrannus "lord, master, tyrant" (cf. Sp. tirano, It. tiranno), from Gk. tyrannos "lord, master, sovereign, absolute ruler," a loan-word from a language of Asia Minor (probably Lydian); cf. Etruscan Turan "mistress, lady" (surname of Venus).
"In the exact sense, a tyrant is an individual who arrogates to himself the royal authority without having a right to it. This is how the Greeks understood the word 'tyrant': they applied it indifferently to good and bad princes whose authority was not legitimate." [Rousseau, "The Social Contract"]
The spelling with -t arose in O.Fr. by analogy with prp. endings in -ant. Fem. form tyranness is recorded from 1590 (Spenser); cf. M.L. tyrannissa (1372).