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Retroactively means in a way: a law or a decision is made to count from a date in the past, not only from today. You use this form when you need an adverb — how the rule applies. “The change will apply retroactively from last June” means last June is treated as the start. Same home as : law, tax, pay, official notices. Though actually, speakers sometimes just say “the raise is to June” and never use this longer form; both are correct, and the shorter adjective is more common in everyday news.
溯及既往地（也常說追溯生效、回溯適用）
組成retroactive + -ly (in that way). From retroactive + -ly.
同家族的字
- retroactivethe adjective; this is that word plus -ly
原始詞典資料1 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
retroactivelyadv/ˌɹɛtɹoʊˈæktɪvli/
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Done after the fact; applying to events that have previously transpired.
- The new legislature passed a resolution retroactively legalizing the actions of the revolutionaries that brought them to power.
- Although it has been already hinted at the link between the human ability to exchange roles and the citizens' right to retroactively adjust unfitting remarks or gestures to the situation, the same connection could perhaps be better[…]
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。