noun

1. An inexperienced recruit, especially in the police or armed forces.

2. A novice.

3. An athlete either new to the sport or to a team or in his first year of professional competition, especially said of baseball, basketball, hockey and American football players.

Synonyms: beginner, newbie, noob, novice, tyro

adjective

1. Non-professional; amateur

   “The game was going well until I made that rookie mistake.”