a.

1. 粗心的，疏忽的；草率的
   He made a careless mistake.

   他犯了一个粗枝大叶的错误。

2. 随便的；自然的
   He sat into a chair with careless ease.

   他随便往椅子里舒舒服服一坐。

3. 漫不经心的；淡漠的[（+of/about）]
   She's careless about her clothes.

   她对穿着一点都不讲究。

4. 无忧无虑的
   careless days

   无忧无虑的日子

adj.

1. not giving sufficient attention or thought to avoiding harm or mistakes.
2. (careless of/about) not concerned or worried about.
   ▸showing no interest or effort; casual.