bone of contention, the

The central point of a dispute. The phrase alludes to two dogs fighting over a single bone, and originally was a bone of dissension (“This became a bone of dissension between these deere friends,” William Lambarde, 1576). The current cliché dates from the early eigh- teenth century, although the metaphor of dogs fighting over a bone had been transferred to human quarrels long before (“The devil hath cast a bone to set stryfe between you,” John Heywood’s Proverbs, 1562).