See dime § Etymology 2
drop a dime (third-person singular simple present drops a dime, present participle dropping a dime, simple past and past participle dropped a dime)
- (idiomatic, slang) To make a telephone call, usually calling authorities to report another's activities.
- He was in the back for a few minutes. Turned out he was dropping a dime on Ralph.
- 1995, Clockers, 00:26:00:
- We got a crowd of black, white customers, out-of-state license plates, what have you. Somebody gonna check that out. They gonna drop a dime on me, call 911. With my jacket, I can't go back to jail.
- (slang, with on) To inform (on).