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indeed; really; absolutely; truly; actually; very; quite
まことに申し訳ございませんが変更は難しいです。
I am truly sorry, but making changes would be difficult.
まことに残念ながら今回は辞退させていただきます。
I regret to say that I have to decline this time.
彼の功績はまことに素晴らしいものだった。
His achievements were truly remarkable.