外快的英文：
extra gains

参考例句：

Lao Zhang has made a huge sum of side money In the past few years
在过去的几年中老张挣了一大笔外快

The money I get from teaching the piano is a useful supplement to my ordinary income.
我教钢琴挣的钱是一笔很管用的外快.

He's been moonlighting for the past year as a driver.
过去一年里他下班后开车赚外快。

extra是什么意思：
adj. 额外的；上好的
n. 额外的事物；另外的收费，额外费用
adv. 特别地，非常；另外，额外地

Is there an extra charge?
有额外的费用吗？

extra interest or excitement
额外的趣味或刺激性的事物

Can I have extra ketchup?
我可以多要一些番茄酱吗？

There are extra trains to the seaside during the summer.
通往海滨的火车在夏季有加车.

This new kind of detergent is of extra strong.
新式去垢剂，具有特效强力。

gains是什么意思：
v. 获得；获利；增加；走快；到达
n. 增加；利润；收获

No pains, no gains.
不劳则无获。

This ticket will gain you admission [will gain admission for you].
这张票将使你得以入场。

Its gain is the product of the gains of its constituent branches.
它的增益等于它含有的分支的增益的积。

This was a campaign that gained momentum.
这是一场势头一直增强的运动。

They gained the game with ease.
他们很轻松地赢得了这场比赛。