In a manner of expressing congratulations or wishes of joy.
Derived from gratulatory (adjective) plus the adverbial suffix -ly, meaning 'in the manner of.' It combines the Latin root gratulari with the English adverbial formation pattern.
This is a word that practically nobody uses anymore—it's so formal and rare that even spell-checkers might not recognize it, yet it appears in older dictionaries as the proper adverbial form of gratulatory.
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