In an aguish manner; with the characteristics of fever, chills, or trembling.
From aguish + -ly (adverbial suffix). Maintains the roots of ague while adding the standard English adverbial ending to create the manner form.
Most words ending in -ly are adverbs, but -ly originally came from Old English 'lic' meaning 'like.' So 'aguishly' literally meant 'in an ague-like way,' showing how grammar itself can tell you a word's history!
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