Marshy, swampy, or resembling a fen; wet and boggy.
From fen (a type of wetland) plus the diminutive suffix -y, creating an adjective. This is a direct descriptive formation that evolved in Middle English to describe land with fen-like qualities.
Shakespeare himself used 'fenny' in Macbeth when describing witches' magical ingredients—'fenny snake' and 'fenny toad'—linking wetland creatures to the dark and mysterious. Fenlands were genuinely treacherous places where people could disappear, making them feel genuinely supernatural to medieval minds.
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