1. He was eating snacks on the sly during class.
他在课堂上偷偷吃零食。

2. They were meeting on the sly to plan the project.
他们偷偷见面来策划这个项目。

3. She bought the gift on the sly so it would be a surprise.
她偷偷买了礼物以制造惊喜。

4. He checked his phone on the sly during the meeting.
他在会议期间偷偷看手机。

A: Why are you smiling on the sly?
A：你为什么偷偷地笑？

B: I was just planning a surprise party on the sly.
B：我只是偷偷在策划一个惊喜派对。

1) 指秘密地、不让他人知道地做事

2) 带有隐秘或略带不正当的行为含义

3) 常用于描述偷偷进行的计划或行动

1. 秘密地；偷偷地

e.g. He was working on the project on the sly.
他在偷偷进行这个项目。

2. 暗中进行地

e.g. She bought the dress on the sly.
她偷偷买了那件裙子。

adverb

1. In a secret or hidden way, without others knowing.

Synonym: secretly, furtively, covertly