He shouldn't spend all his savings frivolously without planning for the future.

### 解释 frivolously 是副词，由形容词 frivolous（轻浮的、不严肃的）加上副词后缀 -ly 构成。frivolous 来自拉丁语 frivolus（无价值的），指做事不认真、随意浪费的行为方式。frivolously 表示"轻率地、随意浪费地"。