firstie

plural firsties

1. USinformalgovernmentA first-class cadet.

   WEST POINT, N.Y., May 22 — The graduating cadets of the United States Military Academy spent their final days here like scores of seniors, or firsties, before them: packing foot lockers and showing their mothers around gray buildings and sweeping lawns.

   2007 May 25, Michael Wilson, “Iraq Presents Graduating Class at West Point With New Challenges”, in New York Times

2. broadlyinformalSomeone who does something for the first time; a debutant or newbie.
3. informalSomeone who is in the first year, or round, of something.
4. slangA First Worlder; someone from the First World.