A US sailor, either enlisted or commissioned officer, who has successfully finished the US Navy nuclear power pipeline and is qualified to operate the nuclear power plants aboard aircraft carriers or submarines.
Prospective nukes are subjected to intense scrutiny and higher standards of behavior and technical knowledge than your standard sailor. They are the elite of the elites.
Nukes often advance quickly through the ranks due to the amount and intensity of training they are subjected to while as a student. Nuke school is widely considered to be one of the toughest schools offered in the military.
1. a Navy term meaning "overthink" that implies you are thinking like a nuke (as defined in the second definition).
2. a person in the Navy, either enlisted or officer, who has had nuclear training and currently works in the field. These people require a higher pre-entrance testing score on their ASVAB (Armed Services Vocational Aptitude Battery) and tend to be smarter than the average person in the Navy, and many times tend to lack common sense.
(for definition 2):
"I just finished training as a nuclear electrician, so now I'm officially a nuke!"
"You're not technically a nuke, but you sure think like one."
"You're such a nuke!"