Ago is used with a time expression to say how far back in the past something happened. It counts backward from the present moment.
From Old English *āgān* meaning “to go away, pass away,” the past participle used in phrases like “gone by.” Over time, it shrank into the simple time word *ago* that we use today.
When you say “two years ago,” you’re literally saying “two years gone (by).” It’s like measuring how much time has ‘walked away’ from you since an event happened.
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