Atrophy means to waste away or become weaker from lack of use. When something atrophies, it shrinks or loses strength because it isn't being exercised or used properly.

The word comes up most often when talking about muscles. If you broke your leg and had to wear a cast for two months, the muscles in that leg would atrophy: they'd become smaller and weaker because they couldn't work during that time. Astronauts in space have to exercise constantly because their muscles will atrophy in the weightless environment where they don't have to work against gravity. Once the cast comes off or the astronaut returns to Earth, those atrophied muscles can be rebuilt through exercise and physical therapy, but it takes time and effort.

The concept applies beyond just muscles. Your brain can atrophy too: if you stop reading challenging books or solving problems, your thinking skills can weaken. A friendship might atrophy if you never spend time together anymore. Even talents can atrophy: a pianist who stops practicing will find their fingers don't move as skillfully as they once did.

The word captures an important truth: abilities and strengths don't stay sharp on their own. They need regular use to stay healthy and strong.

As a noun, atrophy is the weakening or shrinking itself, like muscle atrophy after an injury.