Washout may refer to:

• Washout (erosion), the erosion of a soft surface by a gush of water
• Washout (aeronautics), the practice of building a wing with a twist from root to tip
• Washout (comics), a mutant character in the Marvel Comics universe
• "Washout", a song by The Fallout Trust
• "Washout", a 1991 episode of the PBS show Shining Time Station
• "Washout", a story from The Railway Series book "Thomas Goes Home"
• Washed Out, the stage name of chillwave musician Ernest Greene
• The well drilling process for enlarging a drill hole in an oil well
• A term for a sporting event cancelled due to rain; see Rainout (sports)
• An alternate name for a run-in period, a common phase in clinical research
• Radiocontrast washout, where radiocontrast disappears from a tissue