a.

1. 無用的；無價值的
   The blunt knife is useless.

   這把鈍刀毫無用處。

2. 無效的；無益的
   I realized it was useless to reason with him.

   我知道和他說理是毫無意義的。

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

   當時我的數學差極了。

adj.

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