Just as advice and advise aren’t at all interchangeable, the same can be said about aid and aide. You’ll come across these terms under a range of topic areas, from medicine to government and everything in between.
Aid can be used as both a verb and a noun. As a verb, to aid has roughly the same meaning as to help. You could say, for instance, that you are going to aid the rescue workers after a natural disaster. This kind of usage is more typical in the context of humanitarian efforts, but it is less common (but not incorrect) under more everyday circumstances. You could say that you are aiding someone with their website design, but it may sound odd to native English speakers.
As a noun, aid can refer to assistance in general or it can be used to refer to an inanimate object that assists someone in some way. You may know about hearing aids and first aid, for example. You may have also heard about governments offering foreign aid to developing countries.
Aide, by contrast, would not refer to an inanimate object. Instead, an aide is a human being who is an assistant or helper. Government officials can have many aides, for example, who help them with logistics, research, and so forth. A retirement home will have many aides on staff to help the elderly in a variety of ways. In general, an aide is someone who is closer to the person receiving the assistance rather that someone who is offering help to a larger group of people.
Yes, it’s just one letter and both words are pronounced the exact same way, but you shouldn’t go around talking about “hearing aides” either! As we’ve learned from previous Grammar 101 posts, choosing the right words for the right circumstances can make all the difference.