Definition of "fen"

Caliban: As wicked dewe, as ere my mother bruſh'd / With Rauens feather from vnwholeſome Fen / Drop on you both : A Southweſt blow on yee, / And bliſter you all ore.

1610–1611 (date written), William Shakespeare, “The Tempest”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act I, scene ii], page 4

Milton! thou shouldst be living at this hour: / England hath need of thee: she is a fen / Of stagnant waters […]

1807, William Wordsworth, "England, 1802," collected in Poems (1807)

In dark fens of the Dismal Swamp / The hunted Negro lay; [...]

1842, Henry Wadsworth Longfellow, The Slave in the Dismal Swamp, from Poems on Slavery

He was freezing to death in the flat mud of the Suffolk fens, too proud to go home without a catch.

1986, John le Carré, A Perfect Spy

One poster, which appeared on the Barkhor on 20 May, ridiculed the way neighbourhood committees were recruiting participants: “We paid 30 fen for one stone, but you hire people for 30 yuan for the picnic in the Norbulingka” (“30 fen” — one hundred fen is one yuan — is a joking reference to Chinese accusations that Tibetans were paid 30 fen by splittists for each stone thrown on 1 October 1987).

1994, Ronald David Schwartz, “[Martial Law and After] Symbolic competition”, in Circle of Protest: Political Ritual in the Tibetan Uprising, Delhi: Motilal Banarsidass Publishers Private Limited, published 1996, page 184

Sad to relate, some of the European delegates were probably insurgents rather than true fen. […] But the Europeans could be counted on to take the long view, and many of them would probably turn out to be real fen and fenne after all.

1951 May 21, Winthrop Sargeant, “Through the Interstellar Looking Glass”, in Life‎, volume 30, number 21, page 127

So I’m glad the attached hotel block is entirely reserved for disabled fen! Traveling on mass transit is tiring even when everything’s up to code.

2016 September 3, lurkertype, “Worldcon 75 Chair Responds”, in File 770‎, Comments

[…] whereby the ſtagnating ſap corrupts, and breeds mouldy fen, which often ſpoils whole tracts of, till then, flouriſhing hop-grounds.

1769, The Complete Farmer: Or, a General Dictionary of Husbandry‎, 2nd edition, page 339

Among these are reckoned the wire worm; the flea, and the fly; the fen or mould; the mildew ; and what are usually called fire blasts.

1808, Thomas Potts, The British Farmer's Cyclopaedia or, Complete Agricultural Dictionary‎, Scatcherd and Letterman, page 96

The mould, the fen, or the mouldy-fen, prevails more on hop-grounds which are low, moist, and sheltered, than on such as are high, dry, and open […]

1848, John Marius Wilson, editor, The Rural Cyclopedia‎, volume 2, A. Fullarton, page 698