be broad in the beam

1. Of a ship, to be particularly wide in the middle. Since that ship is broad in the beam, I doubt it will fit through the narrow channel. I'm pretty inexperienced—can I really steer a ship that's so broad in the beam? You think this is broad in the beam? Ha, this is practically a dinghy compared to a real ship!

2. Of a person, to have an ample buttocks. Because I'm broad in the beam, I doubt those pants will fit me. He's a professional athlete—why are you surprised that he's broad in the beam and has legs like tree trunks? I'm a bit broad in the beam after weeks of eating holiday treats.