To retrain means to learn new skills or methods to replace ones you used before, often because your old way of doing things is no longer useful or effective. When a factory worker retrains for a different kind of job after their factory closes, they're learning completely new abilities so they can find work in a different field. When an injured athlete retrains their body to move differently after an injury, they're teaching their muscles new patterns of movement.

The word means replacing or updating knowledge you already had, going beyond simply adding to what you know. A teacher might retrain to use new technology in the classroom, setting aside older methods. A dog owner might need to retrain a puppy that learned bad habits, teaching it the right behaviors to replace the wrong ones.

Retraining often happens because of change: new technology makes old skills obsolete, or circumstances require a different approach. It takes patience and humility because you're essentially becoming a beginner again in an area where you might have felt confident before.