adj. 1. preceding all other objects or events in order, time, or importance; occurring before all other members of a series. Syn. -- first [ WordNet 1.5 +PJC ]
n. 1. a class mail comprising letters, postcards, and other mail sealed against inspection, having a higher priority than second, third, or fourth-class mail; -- it is the highest class of mail not handled in a special manner, as is registered or priority mail. Syn. -- first-class, first-class mail, 1st-class mail [ WordNet 1.5 ]