Think of an old pair of scales. Something has been taken off one side — a loss, an injury, a day of rest that never came — so that side has dropped. Compensatory describes whatever you put on the empty side to bring the two back level. It does not undo what happened, and it is not a punishment for anyone. It is simply the weight that goes in the hole.
From the word’s history
Wiktionary gives the word as borrowed from French compensatoire, and by surface analysis as compensate + -ory. The ending -ory marks something that does the job named by the verb, so the word means, plainly, 'doing the work of making up for something'.
Wiktionary 說這個字借自法文 compensatoire，表面上也可以拆成 compensate（補償）＋ -ory（帶有…作用的）。-ory 表示「負責做那件事的」，所以字面就是「起補償作用的」。兩個意思都還牢牢站在這個字面上，差別只在補的是錢，還是別的東西。
Wiktionary via kaikki extract kaikki:3f6f69a190036ae4:1410883950, entry 'compensatory': "Borrowed from French compensatoire. By surface analysis, compensate + -ory."
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