In a way that takes away from or reduces the value, quality, or reputation of something.
From detract (Latin detrahere 'to draw away') + -ive (adjective suffix) + -ly (adverb suffix). The meaning evolved from the literal 'drawing away' to 'speaking negatively' or 'reducing worth.'
This adverb is rarely used in modern English because 'detractingly' or simply 'negatively' are preferred, but it shows how English allows us to stack suffixes to create precise shades of meaning—though not all combinations survive everyday use.
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