Think of a body that has not been kept well. Something inside has gone wrong, and it stays wrong. Not a scratch that heals by Friday, but a trouble that settles in, makes itself at home, and resists whatever you throw at it. Once that picture is in place, the other uses stop looking like separate words: English lets a speaker point the same word at a city, a school system, or one person's jealousy, because each is being talked about as a body that is quietly, chronically .
From the word’s history
The evidence packet traces malady to Old French maladie (sickness), from malade (ill), from Latin male habitus, literally 'ill-kept, not in good condition'. The oldest layer is therefore not the name of a disease but a judgement on a state: this body is not being held in good condition. That is exactly the picture the modern uses still lean on.
證據顯示 malady 來自古法文 maladie（生病）、malade（生病的），再往前是拉丁文 male habitus，字面上是「被弄得很糟、狀況不好」。所以最早那一層並不是某個病的名字，而是對一個狀態的判斷：這個身體沒有被維持好。今天的各種用法，靠的還是同一個畫面。
Wiktionary, "malady"
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