The Collaborative International Dictionary of English v.0.48:

Supple \Sup"ple\, v. i.
   To become soft and pliant.
   [1913 Webster]

         The stones . . .
         Suppled into softness as they fell.      --Dryden.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Supple \Sup"ple\ (s[u^]p"p'l), a. [OE. souple, F. souple, from
   L. supplex suppliant, perhaps originally, being the knees.
   Cf. Supplicate.]
   1. Pliant; flexible; easily bent; as, supple joints; supple
      fingers.
      [1913 Webster]

   2. Yielding; compliant; not obstinate; submissive to
      guidance; as, a supple horse.
      [1913 Webster]

            If punishment . . . makes not the will supple, it
            hardens the offender.                 --Locke.
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   3. Bending to the humor of others; flattering; fawning;
      obsequious. --Addison.
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   Syn: Pliant; flexible; yielding; compliant; bending;
        flattering; fawning; soft.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Supple \Sup"ple\, v. t. [imp. & p. p. Suppled (s[u^]p"p'ld);
   p. pr. & vb. n. Suppling (s[u^]p"pl[i^]ng).]
   1. To make soft and pliant; to render flexible; as, to supple
      leather.
      [1913 Webster]

            The flesh therewith she suppled and did steep.
                                                  --Spenser.
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   2. To make compliant, submissive, or obedient.
      [1913 Webster]

            A mother persisting till she had bent her daughter's
            mind and suppled her will.            --Locke.
      [1913 Webster]

            They should supple our stiff willfulness. --Barrow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

supple
    adj 1: moving and bending with ease [syn: lissome, lissom,
           lithe, lithesome, slender, supple, svelte,
           sylphlike]
    2: (used of e.g. personality traits) readily adaptable; "a
       supple mind"; "a limber imagination" [syn: limber,
       supple]
    3: (used of persons' bodies) capable of moving or bending freely
       [syn: limber, supple]
    v 1: make pliant and flexible; "These boots are not yet suppled
         by frequent use"

Moby Thesaurus II by Grady Ward, 1.0:

145 Moby Thesaurus words for "supple":
   Machiavellian, Machiavellic, able to adapt, accommodating,
   acquiescent, acute, adaptable, adjustable, agile, all-around,
   alterable, alterative, ambidextrous, amphibious, arch, artful,
   astute, athletic, bendable, bending, cagey, canny, changeable,
   checkered, clever, complaisant, compliant, crafty, cunning, cute,
   deceitful, deep, deep-laid, designing, diplomatic, ductile,
   elastic, ever-changing, extensible, extensile, fabricable, facile,
   fawning, feline, fictile, flexible, flexile, flexuous, fluid,
   formable, formative, foxy, generally capable, giving, graceful,
   guileful, impermanent, impressible, impressionable, ingenious,
   ingratiating, insidious, inventive, kaleidoscopic, knowing,
   like putty, limber, lissome, lithe, lithesome, malleable,
   many-sided, metamorphic, mobile, modifiable, moldable, movable,
   mutable, nimble, nonuniform, obliging, obsequious, pawky,
   permutable, plastic, pliable, pliant, politic, protean, proteiform,
   ready, receptive, resilient, resourceful, responsive, rubbery,
   scheming, sensitive, sequacious, serpentine, servile, shapable,
   sharp, shifty, shrewd, slick, slippery, sly, smooth, snaky, sneaky,
   sophistical, springy, stealthy, strategic, stretch, stretchy,
   submissive, subtile, subtle, susceptible, tactical, temporizing,
   timeserving, toadying, tractable, tractile, transient, transitory,
   trickish, tricksy, tricky, trimming, two-handed, unresistant,
   unresisting, variable, versatile, vulpine, wary, whippy, willowy,
   wily, wiry, yielding