用作形容词：
较低的，下面的
A cloth should be spread under.
下面该铺一块布。
用作副词：
1、在下面，在水下
As a matter of fact, Jesse's wife did soon go under.
事实上，杰西的妻子不久便降低了身份。
2、少于，小于，较年轻
Nearly half of mothers with children under five have a job.
孩子不满5岁的妈妈中近一半有工作。
You should choose these jobs for those under 65.
你应该选择适合65岁以下人士的工作。