One who snitches or informs on someone to a person of higher authority. Originally street slang for someone who informs to the police, it refers to the old price of using a public payphone (10 cents). Primarily heard in US, South Africa. I bet Timmy's the dime-dropper—he's such a teacher's pet, always ready to tattle on any of the other students he thinks are misbehaving. He knew he was facing 10 years in prison, so he agreed to be a dime-dropper for the police in exchange for a lighter sentence.