underside
noun [ C usually singular ] uk/ˈʌn.də.saɪd/ us/ˈʌn.dɚ.saɪd/
下面；底部
the side of something that is usually closest to the ground
The car had turned over in the ditch, and its underside was covered in oil and mud. 车翻倒在沟里了，车底上满是油污和泥巴。
Synonym: bottom