sinister 1411, "prompted by malice or ill-will," from O.Fr. sinistre "contrary, unfavorable, to the left," from L. sinister "left, on the left side" (opposite of dexter), perhaps from base *sen- and meaning prop. "the slower or weaker hand" [Tucker], but Buck suggests it's a euphemism (see left), connected with the root of Skt. saniyan "more useful, more advantageous." The L. word was used in augury in the sense of "unlucky, unfavorable" (omens, especially bird flights, seen on the left hand were regarded as portending misfortune), and thus sinister acquired a sense of "harmful, unfavorable, adverse." This was from Gk. influence, reflecting the early Gk. practice of facing north when observing omens; in genuine Roman auspices, the left was favorable. Bend (not "bar") sinister in heraldry indicates illegitimacy and preserves the lit. sense of "on the left side."