In a manner that deviates; while turning aside or departing from a standard course or expected path.
From deviate + -ly adverbial suffix. The adverb form modifies verbs or adjectives to describe how deviation occurs.
Deviately is such a rare adverb that you'll almost never see it in modern writing—most writers would say 'in a deviating manner' or simply 'deviantly.' It's a word that technically exists but sits unused on the shelf of English.
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