An inexperienced recruit, especially in the police or armed forces.
"The rookie officer was nervous as he stepped onto his first patrol beat alone."
In plain English: A rookie is someone who has just started doing something new and doesn't have much experience yet.
"The rookie made a mistake on his first day at work, but he quickly learned from his boss."
Usage: Use "rookie" to describe someone new and inexperienced in their job rather than referring to a person's general lack of skill. It is most commonly applied to recruits entering professions like law enforcement or military service, though it can also function as an adjective for any non-professional activity.
non-professional; amateur
"The rookie volunteer firefighter helped direct traffic until the professional crews arrived."
The word likely comes from "recruit" with the diminutive suffix "-ie," though some suggest it may derive from Dutch or Irish words meaning an inexperienced boy. Regardless of its exact source, it entered English to describe a new or untrained member of any group.