I think the relevant legal mechanism would be a trademark, and in order for it to be a legal issue, you would need to be operating in the same business space as

I think the relevant legal mechanism would be a trademark, and in order for it to be a legal issue, you would need to be operating in the same business space as an existing registered trademark holder (because then you might cause confusion between yours and their products/services). Copyright generally doesn't apply in the case of a single word.