n.

1. 恩惠
   Your donation to the hospital was really a boon to those poor patients.

   你给医院的捐赠对于那些贫穷的病人来说是真正的恩惠。

2. 利益
   Many people think that the new Disney World is a great boon to the fortunes of Shanghai.

   许多人认为，新的迪士尼公园是上海财政的一大利益。

a.

1. 快活的，欢乐的，令人愉悦的
2. 慷慨的

n.

1. a thing that is helpful or beneficial.
2. archaic a favour or request.