一般表示所修饰名词事物的用途。例如：
a writing desk=a desk for writing
写字台
a swimming pool=a pool swimming
游泳池
有些动名词作定语，与所修饰的名词关系比较复杂。例如：
boiling point=a temperature point at which something begins to boil
沸点
a walking tractor=a tractor which a driver can operate while he or she is walking behind it
手扶拖拉机
