- On leaving the hospital, the patient felt almost too weak to walk, but he soon overcame this infirmity.
debilitate 使虚弱 （反义词：invigorate）
- The patient had been so debilitated by the fever that he lacked the strength to sit up.
- Enervated by the heat, we rested under a shady tree until our strength was restored.
- Ruth will be absent today. She is incapacitated by a sore throat.
- When industry moves away, a flourishing town may quickly become decadent.
decrepit 老朽的 （反义词：sturdy）
- Bill rode past the street on a horse that looked decrepit and about to collapse.
- Up the road was an abandoned farmhouse, partially in ruins, and near it a barn, even more dilapidated.
- Judy understands algebra well but I have only a flimsy grasp of the subject.
frail 虚弱的 （反义词：robust）
- To be an astronaut, you must be in robust health. It is not an occupation for a frail person.