The main thing is the most important one of several similar things in a particular situation.
one of the main tourist areas of San Francisco.
旧金山的主要旅游区之一。
My main concern now is to protect the children.
我现在最关心的是保护这些孩子。
Our main objective was to improve safety.
我们的主要目标是提高安全性。
What are the main differences and similarities between them?
它们主要的相同之处及不同之处在哪里?
mains
The mains are the pipes which supply gas or water to buildings, or which take sewage away from them.
the water supply from the mains.
总管道的水供应。
in the main
If you say that something is true in the main, you mean that it is generally true, although there may be exceptions.
Tourists are, in the main, sympathetic people.
游客们大都是有同情心的人。