To inform; give information, esp to the police; dime, rat •New York City teenagers have equated dime with an amount of information and also speak of dropping a quarter, more information, and dropping a dollar, the maximum of information: Chaney questioned the man who had dropped the dime on Madison/ And then he dropped the dime (made the phone call) and turned Vinnie in(1960s+)
To point out the faults and failures of another; criticize (1970s+ Army)
[fr the dime put into a pay telephone in that era]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with drop a dime
Inform on or betray someone, as in No one can cheat in this class—someone's bound to drop a dime and tell the teacher. This expression, alluding to the ten-cent coin long used for making a telephone call, originated as underworld slang for phoning the police to inform on a criminal and occasionally is extended to any kind of betrayal.