First is number one, prior to, or before. First comes first, then comes everything else. It's always good to be first in line or in first class. Who wants to be second? Or worse — last?
Whether it’s a noun, adjective, or adverb, you’ll find first at the beginning and opposite from last. And whether you’ve won first place or have just become the First Lady, first usually indicates a good thing — unless of course you're first to be fired. That doesn’t answer the Abbott and Costello question “Who's on first?” though.