The Collaborative International Dictionary of English v.0.48:

Tendril \Ten"dril\, n. [Shortened fr. OF. tendrillon, fr. F.
   tendre tender; hence, properly, the tender branch or spring
   of a plant: cf. F. tendrille. See Tender, a., and cf.
   Tendron.] (Bot.)
   A slender, leafless portion of a plant by which it becomes
   attached to a supporting body, after which the tendril
   usually contracts by coiling spirally.
   [1913 Webster]

   Note: Tendrils may represent the end of a stem, as in the
         grapevine; an axillary branch, as in the passion
         flower; stipules, as in the genus Smilax; or the end of
         a leaf, as in the pea.
         [1913 Webster]
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tendril \Ten"dril\, a.
   Clasping; climbing as a tendril. [R.] --Dyer.
   [1913 Webster] Tendriled

WordNet (r) 3.0 (2006):

tendril
    n 1: slender stem-like structure by which some twining plants
         attach themselves to an object for support

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "tendril":
   animal fiber, appendage, arm, artificial fiber, bine, bough,
   branch, branchedness, branchiness, burgeon, capillament, cilium,
   cirrus, cobweb, coil, corkscrew, curl, curlicue, deadwood, denier,
   evolute, fiber, fibrilla, filament, filamentule, flagellum, fork,
   frond, gossamer, gyre, hair, hand, hank, helix, imp, involute,
   joint, kink, leg, limb, link, lobe, lobule, member, offshoot,
   organ, pinion, ramage, ramification, ringlet, roll, runner,
   sarment, scion, screw, scroll, shoot, skein, slip, spear, spiral,
   spray, sprig, sprit, sprout, spur, stolon, strand, sucker, suture,
   swirl, switch, tail, thallus, thread, threadlet, twig, twirl,
   twist, volute, volution, vortex, web, whirl, whorl, wing