The Collaborative International Dictionary of English v.0.48:

Fern \Fern\, adv.
   Long ago. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fern \Fern\, a. [AS. fyrn.]
   Ancient; old. [Obs.] "Pilgrimages to . . . ferne halwes."
   [saints]. --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Fern \Fern\ (f[~e]rn), n. [AS. fearn; akin to D. varen, G. farn,
   farnkraut; cf. Skr. par[.n]a wing, feather, leaf, sort of
   plant, or Lith. papartis fern.] (Bot.)
   An order of cryptogamous plants, the Filices, which have
   their fructification on the back of the fronds or leaves.
   They are usually found in humid soil, sometimes grow
   epiphytically on trees, and in tropical climates often attain
   a gigantic size.
   [1913 Webster]

   Note: The plants are asexual, and bear clustered sporangia,
         containing minute spores, which germinate and form
         prothalli, on which are borne the true organs of
         reproduction. The brake or bracken, the maidenhair, and
         the polypody are all well known ferns.
         [1913 Webster]

   Christmas fern. See under Christmas.

   Climbing fern (Bot.), a delicate North American fern
      (Lygodium palmatum), which climbs several feet high over
      bushes, etc., and is much sought for purposes of
      decoration.

   Fern owl. (Zool.)
   (a) The European goatsucker.
   (b) The short-eared owl. [Prov. Eng.] -- Fern shaw, a fern
      thicket. [Eng.] --R. Browning.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fern
    n 1: any of numerous flowerless and seedless vascular plants
         having true roots from a rhizome and fronds that uncurl
         upward; reproduce by spores

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "fern":
   Calamites, Cycadofilicales, Filicales, Selaginellaceae, Sigillaria,
   algae, autophyte, bean, bracken, brown algae, calamite, climber,
   conferva, confervoid, creeper, cycadofilicales, diatom, equisetum,
   filicoids, fruits and vegetables, fucus, fungus, grapevine,
   green algae, gulfweed, herb, heterophyte, ivy, kelp, legume,
   lentil, lepidodendrids, lepidodendroids, liana, lichen, liverwort,
   mold, moss, mushroom, parasite, parasitic plant, pea, perthophyte,
   phytoplankton, planktonic algae, plant families, puffball, pulse,
   red algae, rockweed, rust, saprophyte, sargasso, sargassum,
   sea lentil, sea moss, sea wrack, seaweed, smut, succulent,
   toadstool, vetch, vine, wort, wrack