mump

例句：

1. 1. She sat on the couch with her buttocks sticking out.
   她坐在沙发上，屁股凸出。
2. 2. The doctor examined his patient's sacrum for any signs of injury.
   医生检查了病人的骶骨，看是否有受伤的迹象。
3. 3. He had a lump on his buttocks that he thought might be cancer.
   他屁股上有个肿块，他觉得可能是癌症。