Meaning of fast one

fast' one"

Pronunciation: [key]
— Informal. Informal.
  1. a shrewd action, esp. when unscrupulous or dishonest; an unfair trick, deceitful practice, dishonest dealing, etc.: He pulled a fast one on me by paying me with a worthless check.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.