This is the 406th most frequent Japanese word.
すでに
Already.
すでに (sudeni) is used here to indicate that the action of departure has been completed before the current moment.
彼はすでに出発しました。
He has already departed.
すでに (sudeni) is used to highlight that the resolution occurred at an earlier time.
その問題はすでに解決済みだ。
That issue has already been resolved.
すでに (sudeni) is employed to stress that the knowledge of the matter was acquired prior to this moment.