The Collaborative International Dictionary of English v.0.48:

Creeper \Creep"er\ (kr[=e]p"[~e]r), n.
   1. One who, or that which, creeps; any creeping thing.
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            Standing waters are most unwholesome, . . . full of
            mites, creepers; slimy, muddy, unclean. --Burton.
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   2. (Bot.) A plant that clings by rootlets, or by tendrils, to
      the ground, or to trees, etc.; as, the Virginia creeper
      (Ampelopsis quinquefolia).
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   3. (Zool.) A small bird of the genus Certhia, allied to the
      wrens. The brown or common European creeper is Certhia
      familiaris, a variety of which (var. Americana) inhabits
      America; -- called also tree creeper and creeptree.
      The American black and white creeper is Mniotilta varia.
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   4. A kind of patten mounted on short pieces of iron instead
      of rings; also, a fixture with iron points worn on a shoe
      to prevent one from slipping.
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   5. pl. A spurlike device strapped to the boot, which enables
      one to climb a tree or pole; -- called often telegraph
      creepers.
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   6. A small, low iron, or dog, between the andirons.
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   7. pl. An instrument with iron hooks or claws for dragging at
      the bottom of a well, or any other body of water, and
      bringing up what may lie there.
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   8. Any device for causing material to move steadily from one
      part of a machine to another, as an apron in a carding
      machine, or an inner spiral in a grain screen.
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   9. pl. (Arch.) Crockets. See Crocket.
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WordNet (r) 3.0 (2006):

creeper
    n 1: any plant (as ivy or periwinkle) that grows by creeping
    2: a person who crawls or creeps along the ground [syn:
       crawler, creeper]
    3: any of various small insectivorous birds of the northern
       hemisphere that climb up a tree trunk supporting themselves
       on stiff tail feathers and their feet [syn: creeper, tree
       creeper]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "creeper":
   algae, autophyte, bean, bracken, brown algae, climber, conferva,
   confervoid, diatom, fern, fruits and vegetables, fucus, fungus,
   grapevine, green algae, gulfweed, herb, heterophyte, ivy, kelp,
   legume, lentil, 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