Username Vs. Nickname, can nicks be unique?

I’m a new user of WP. Is there any way to effectively eliminate duplication of used nicknames? Perhaps if for users, nickname was locked to match the username, making it unique? Maybe then allow only authors to have nicks (that were then also locked out of the general pool of available names). Hoping this was a setting that I’m just not seeing, or maybe a hack/plug-in that could be used.
Thanks! WP is great.