fen1 Syllabification: (fen)Pronunciation: /fen/Translate fen | into Italian Definition of fen noun a low and marshy or frequently flooded area of land:a flooded fen 55 acres of fen (the Fens) flat low-lying areas of eastern England, formerly marshland but largely drained for agriculture since the 17th century. Ecology wetland with alkaline, neutral, or only slightly acid peaty soil. Compare with bog.Derivatives fenny adjective Origin: Old English fen(n)fen in other Oxford dictionaries Definition of fen in the British & World English dictionary