Stunt has two main meanings:

1. To slow or stop something's natural growth or development. When plants don't get enough water or sunlight, their growth becomes stunted, meaning they stay small and weak instead of reaching their full size. Poor nutrition can stunt a child's growth. Sometimes people talk about how constant criticism might stunt someone's confidence, keeping them from becoming as bold or capable as they could be.
2. A difficult, dangerous, or unusual physical feat performed to entertain or impress others. When you watch an action movie and see someone jump from a moving car or leap between buildings, that's usually a stunt performed by a professional stunt performer (often called a stunt double, who fills in for the actor). Skateboard tricks, motorcycle jumps, and acrobatic flips can all be stunts. Sometimes people pull publicity stunts to get attention, like when a business owner does something outrageous to get on the news. The word can carry a slightly dismissive tone in this usage, suggesting something showy but not necessarily meaningful.