In a manner that expresses praise, approval, or recommendation.
From commendatory (adjective, expressing praise) plus the adverbial suffix -ly, which converts adjectives to adverbs describing how something is done.
This adverb is so rare that most people would just say 'in a praising way' instead—it's the kind of word that shows up in 19th-century British novels but almost nowhere else in modern writing.
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