Describe something as atrophied if it's shrunken or made smaller and weaker because of illness. If you've ever had a broken arm, you know that after months inside a cast your muscles become somewhat atrophied.
Medically, when a body part is atrophied, it's started to waste away. Arms and legs can become atrophied from injury or disuse, and even internal organs can be atrophied when they're affected by disease. People who don't have enough food to eat eventually develop atrophied bodies, diminished by lack of nutrition. The Greek root is atrophia, "a wasting away," from a, "not," and trophe, "nourishment."