In a manner that shows irritability and complaints; in a grouchy way.
Formed from 'grouching' (the gerund/adjective form) plus the adverbial suffix -ly, which converts adjectives and participles into adverbs describing how an action is performed.
This word is a linguistic nesting doll—it takes 'grouch,' adds -ing to make it an adjective, then adds -ly to make an adverb, showing how English builds complex shades of meaning by stacking suffixes.
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