BROAD IN THE BEAM
The somewhat derogatory phrase used to describe someone who has wide hips or buttocks originates from the nautical term for the widest point of a ship –the beam or beame.
Although the phrase dates back at least to the 1620’s the figurative use did not come into play until the 20th Century as in an early citation from Hugh Walpole's Hans Frost, 1929, 'He stood watching disgustedly Bigges' broad beam.'