An archaic or obsolete spelling/form of 'haughtily'; in a haughty manner.
An older adverbial form of 'haughty,' before standard '-ly' adverbial suffixes became fully regularized in English.
Haughtly is a spelling you'd find in Renaissance texts—it shows how English adverbs weren't always standardized, and scribes played around with different forms until conventions settled down.
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