CIDE DICTIONARY
fen, n. [AS. fen, fenn, marsh, mud, dirt; akin to D. veen, OFries. fenne, fene, OHG. fenna, G. fenn, Icel. fen, Goth. fani mud.].
Low land overflowed, or covered wholly or partially with water, but producing sedge, coarse grasses, or other aquatic plants; boggy land; moor; marsh. [
1913 Webster]
" Fen is used adjectively with the sense of belonging to, or of the nature of, a fen or fens."
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"'Mid reedy fens wide spread."
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Fen boat, a boat of light draught used in marshes. -- Fen duck (Zoöl.), a wild duck inhabiting fens; the shoveler. [Prov. Eng.] -- Fen fowl (Zoöl.), any water fowl that frequent fens. -- Fen goose (Zoöl.), the graylag goose of Europe. [Prov. Eng.] -- Fen land, swamp land.
ROGET THESAURUS
fen
Marsh
N
marsh, swamp, morass, marish, moss,
fen, bog, quagmire, slough, sump, wash, mud, squash, slush, baygall, cienaga, jhil, vlei, marsh, marshy, swampy, boggy, plashy, poachy, quaggy, soft, muddy, sloppy, squashy, paludal, moorish, moory, fenny.