American Heritage Dictionary of the English Language, 5th Edition
Old English fenn, from Proto-Germanic*fanją (cf. West Frisian fean, Dutch veen, Norwegian fen), from Proto-Indo-European*pen ‘bog, mire’ (cf. Middle Irish en ‘water’, enach ‘swamp’, Old Prussian pannean ‘peat-bog’, Sanskrit pánkas ‘marsh, mud’).
From fan, by analogy with men as the plural of man
Fen Sentence Examples
The south-eastern portion of the province consists of high fen resting on diluvial sand.
It lies in the midst of the flat fen country.
The word was derived in antiquity from the town of Helos in Laconia, but is more probably connected with 'Aos, a fen, or with the root of AEiv, to capture.
The western division consists of low fen or clay soil and presents a monotonous expanse of rich meadow-land, carefully drained in regular lines of canals bordered by stunted willows, and dotted over with windmills, the sails of canal craft and the clumps of elm and poplar which surround each isolated farm-house.