noun

• (loosely) Any swamp or mire (especially with negative connotations).
  "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."

noun

• (fandom slang) a plural of fan used by enthusiasts of science fiction, fantasy, and anime, partly from whimsy and partly to distinguish themselves from fans of sport, etc.
  "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."

noun

• (furry fandom, Internet slang, informal) A fennec fox.
  "Your fursona holding mine while she's arguing with some random person Like you're cradling the little fen & she's screaming out threats"

intj

• (obsolete) Used in children's games to prevent or forestall another player's action; a check or bar.