A Trademark is a Mark that is used in Trade. The mark can be a word, such as “Apple”, it can be a picture, such as the Apple logo, or a phrase such as “finger licking good”. Any person or company acquires a trademark by using their mark in trade. They may also register their mark in any number of places. The same Mark may be claimed/held/registered by a number of companies Trading in different industries and places.
A copyright is a right that protects creative works. Creative works could be a book, a movie, painting, a website design, website content, even a building design.
“Copyright does not protect names, titles, slogans, or short phrases” --US Copyright Off. So "Nick Of Time" is not copyrighted. The movie is, but don't worry about having to pay Johnny Depp a nickel every time you say “He got there in the nick of time”
So in the context of a domain name copyright is largely irrelevant. The name is simply not “long enough”. Where copyright is an issue for a domain name is when a word of phrase has trademark protection because it is associated with a certain work. For example, you can't simply register the name of every major place and character in this weeks top selling book because those names have become trademarks.