Showing or expressing disdain; in a disdainful manner (archaic/rare form).
From disdain + -ly (suffix creating adjectives/adverbs). This is an older formation competing with 'disdainful,' which eventually became standard.
Disdainly' is so archaic it barely appears in modern texts—it lost the competition to 'disdainful,' showing how English gradually standardizes on one form even when multiple options exist.
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