aid

n. 帮助,有帮助的事物
v. 援助,帮助
abbr.=Agency for International Development 国际开发署[美]

A dictionary is an invaluable aid in learning a new language.

在学习一种新语言时，词典是非常有用的工具。

We were greatly aided in our investigation by the cooperation of the police.

我们在调查的过程中得到警方的大力协助。