Noun

1. a narcotics squad police officer.
2. - a person who notifies authorities of illicit activity, betraying someone in the process.

Verb

1. - to inform authorities of the illicit actions of others that one has knowledge of as an insider

   "If you narc on me, I'll rip your arms off," said Tim to his little brother, as he passed him a cigarette.

2. to suffer from impaired judgment due to nitrogen narcosis (e.g. while scuba diving).