From Old English (before 12th century), from Proto-Indo-European '*pen-' ("swamp, water, wet"), from PIE *pen- ("swamp, wet").
A low and marshy or frequently flooded area of land; a type of wetland fed by mineral-rich surface or ground water.
From Old English 'fenn' (mud, mire, dirt; a fen, marsh, moor), from Proto-Germanic '*fanją' (fen, swamp, mud), from PIE root *pen- (swamp, water, wet). The word is specifically English and Frisian — the Fens of East Anglia are the landscape that kept this word alive. Before the great drainage works of the 17th century under Cornelius Vermuyden, the Fens were a vast waterlogged wilderness where isolated communities lived on islands
Boston's Fenway Park sits on land that was literally a 'fen way' — a path through the marshy Back Bay fens. The Fens neighborhood was built on filled-in wetland in the 1880s. So when you hear 'Fenway,' you are hearing an Old English word for 'swamp road' — a thousand-year-old description that remains geographically accurate.