The words aid and aide sound identical, but their meanings are very different.
(Note: Aid and aide are homonyms, i.e., pronounced the same but with different meanings.)

Aid
The word aid means help or assistance. It is commonly seen as an adjective, a noun, or a verb. (As a verb, it means to help or to assist.)

Be bold and mighty powers will come to your aid.
I have known sorrow and learned to aid the wretched.  

Aide
The noun aide means a helper or an assistant. An aide is a person.

General McChrystal and his aides told the unvarnished truth.
The Libyan leader caused a scene at the African Heads of State Summit in Munyonyo when he slapped one of his aides for taking him to a wrong venue.  

Source: grammar-monster.com