apple of discord An object or source of dispute; a bone of contention. Eris, Greek goddess of discord, angry at not having been invited to the wedding of Peleus and Thetis, sought to foment discord among the wedding guests. She threw into their midst a golden apple inscribed “for the fairest.” When Hera, Pallas Athena, and Aphrodite each laid claim to the apple, Paris was called upon to decide the issue. He awarded the apple to Aphrodite, thus bringing upon himself the vengeance of the other two goddesses, to whose spite is attributed the fall of Troy.

at loggerheads At odds, in disagreement, quarreling. Although numerous explanations have been offered, the origin of this expression remains obscure. The OED suggests that a loggerhead (a long-handled instrument for melting pitch and heating liquids) may have been formerly used as a weapon.

at sixes and sevens See DISORDER.

bone of contention A subject of disagreement or dispute; a cause of discord. This expression is an expanded version of the simpler bone from the phrase cast a bone between. The discord created when a single bone is thrown among several dogs is the obvious source.

a crow to pluck A dispute or disagreement; a bone to pick. Of unknown origin, this expression appeared as early as 1460 in the Towneley mysteries; its earliest version was a crow to pull.