1
the underside of [something]
The underside of the leaf is green.
叶子的底面是绿色的。
底面；下侧；底部
先理解核心含义，再看它在真实句子里的用法。
底面；下侧；底部
the side that is below or underneath; the bottom
The underside of the leaf is green.
叶子的底面是绿色的。
下面
The side that is below or underneath, the bottom.
The label is on the underside of the bottle.
标签在瓶子的底部。
A thin layer of paint covers the underside of the bridge.
桥的底部覆盖着一层薄漆。
We found a crack on the underside of the table.
我们在桌子的底面发现了一道裂缝。
The underside of the leaf is green.
叶子的底面是绿色的。
There is a sticker on the underside of the table.
桌子下面有一张贴纸。
He examined the object from the underside.
他从下面检查了这个物体。
Not this
Underside of the leaf is green.
Use this
The underside of the leaf is green.
中文中常省略冠词，但英语可数名词单数前需要定冠词 'the' 来指代特定事物。
Not this
The under of the box is wet.
Use this
The underside of the box is wet.
学习者误将介词 'under' 当作名词使用，应为名词 'underside' 表示底面。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
叶子的背面
The aphids were clustered on the underside of the leaf.
蚜虫聚集在叶子的背面。
岩石的底面
We found a salamander hiding under the underside of a rock.
我们发现一只蝾螈躲在岩石的底面下。
汽车的底盘
The mechanic inspected the underside of the car for rust.
机械师检查了汽车的底盘是否有锈蚀。
桥的底面
Bats roost on the underside of the bridge during the day.
蝙蝠白天栖息在桥的底面。
下巴的下侧
He had a small scar on the underside of his chin.
他下巴的下侧有一个小疤痕。
Use underside naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
拆分记忆：under（下）+ side（边），即底边、下面。
语域：mixed 常见场景：technical description、everyday usage “underside”常用于正式或技术性描述（如物体底面），也常见于日常口语中指物体的下方，因此语域为混合。
All listed words end with -side and share the same pronunciation /saɪd/ (with possible stress variation), forming perfect rhymes with 'underside'.
Dictionary facts from ECDICT, WIKTIONARY, WORDNET.