To pay a bribe to someone, typically an authority figure such as a judge or cop. Generally used with the subject, e.g. "slip the cop a few bucks", etc.
Jeff: What should I do if they catch me?
Luke: Slip a few bucks to the judge, you'll get a light sentence.

Megan: How'd you get out of jail?
Josh: I slipped the guard a few bucks to leave a door open
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