During my winter break I had the same argument twice, about definitions. People said that definitions can be disproved, and I said that that doesn’t make sense, since definitions have no truth value.

What do you call a definition (haha, define “definition”)? To put it simply, it’s giving something a name. The thing is described, and a name is assigned to that description. So a definition has no truth value, it’s just a naming. It can’t be true or false, it can only be different from other definitions (whether of the same term or the same thing is irrelevant).