Resembling, containing, or covered with coal dust or slack coal; dark and dusty like coal.
Derived from coom with the addition of the -y suffix, a common English pattern for turning nouns into adjectives meaning 'having the quality of' or 'resembling.'
Mining regions developed such specific descriptive vocabulary—a 'coomy' surface meant something very particular to miners and their families, a word that perfectly captured the gritty reality of industrial life.
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