a.

1. 无用的；无价值的
   The blunt knife is useless.

   这把钝刀毫无用处。

2. 无效的；无益的
   I realized it was useless to reason with him.

   我知道和他说理是毫无意义的。

3. 【口】（人）无能的，没有用的
   I was useless at maths.

   当时我的数学差极了。

adj.

1. serving no purpose.
2. informal having little ability or skill.