When I am online, my favorite way to get a definition of a word is to search for it on google.com . A google search for “appropriate” will list “relevant” as one of the synonyms of its adjective form. Both of those words basically have the same meaning. To say that something is relevant or appropriate to something is to say that there is some connection, relation, or link between it and something else. By this, we can know that the word “inappropriate” is literally a synonym for “irrelevant”.
A Chihuahua and a Saint Bernard are both called dogs but what is the connection? Is it because they both have four legs? Wouldn’t that make them the same as cats, horses, or elephants? After a bit of reading, I found that there are so many things that all the dogs have in common. I read that they evolved from the Gray Wolf. The point is that they are all related, relevant, or appropriate to each other. If you are looking for a pet that barks, howls, and growls, then you should use the word “dog” when searching the internet or speaking to someone about it. It is the appropriate word. To ask for an elephant would be inappropriate.
People use the word inappropriate in a way that is inappropriate! They use it as if it means that someone is doing something wrong according to their own moral standard. Irrelevant means the same thing as inappropriate, but at least it is not used in the same way traditionally.