The quality, character, or condition of being dull; dullness (archaic or rare).
From 'dull' + the suffix '-ery' (a place, practice, or collection of things, as in 'gallery' and 'archery'). This word is rarely used in modern English but follows a productive pattern for creating abstract nouns.
Dullery is such a strange word—the '-ery' suffix usually makes concrete nouns like 'archery' (the place/practice of arrows) and 'pottery' (the place/practice of pots), but here it creates an abstract quality!
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