Resembling flannel in texture, appearance, or quality; soft and warm like flannel.
From flannel plus the adjectival suffix -y, creating an adjective meaning 'like or having the quality of flannel.'
Words ending in -y are often the English language's shorthand for 'resembling or having the quality of'—flannelly, woolly, fluffy all work the same way to turn nouns into quick descriptive adjectives.
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