The Collaborative International Dictionary of English v.0.48:

Rusty \Rust"y\, a. [AS. rustig.] [Compar. Rustier; superl.
   Rustiest.]
   1. Covered or affected with rust; as, a rusty knife or sword;
      rusty wheat.
      [1913 Webster]

   2. Impaired by inaction, disuse, or neglect.
      [1913 Webster]

            [Hector,] in this dull and long-continued truce,
            Is rusty grown.                       --Shak.
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   3. Discolored and rancid; reasty; as, rusty bacon.
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   4. Surly; morose; crusty; sullen. [Obs. or Prov. Eng.] "Rusty
      words." --Piers Plowman.
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   5. Rust-colored; dark. "Rusty blood." --Spenser.
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   6. Discolored; stained; not cleanly kept; filthy.
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            The rusty little schooners that bring firewood from
            the British provinces.                --Hawthorne.
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   7. (Bot.) Resembling, or covered with a substance resembling,
      rust; affected with rust; rubiginous.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rusty
    adj 1: covered with or consisting of rust; "a rusty machine";
           "rusty deposits"
    2: of the brown color of rust [syn: rust, rusty, rust-
       brown]
    3: impaired in skill by neglect [syn: out of practice(p),
       rusty]
    4: ancient; "hoary jokes" [syn: hoary, rusty]

Moby Thesaurus II by Grady Ward, 1.0:

182 Moby Thesaurus words for "rusty":
   Titian, Titian-red, a stranger to, adust, anile, auburn, bay,
   bay-colored, bayard, brazen, bricky, bronze, bronze-colored,
   bronzed, brownish-red, cardinal, carmine, carnation, carnelian,
   castaneous, cerise, cherry, cherry-colored, cherry-red, chestnut,
   chestnut-brown, copper, copper-colored, coppery, corroded, crabbed,
   crimson, crumbling, cupreous, damask, debilitated, decrepit,
   dilapidated, disaccustomed, doddered, doddering, doddery, dry,
   dusty, dyspeptic, eaten, eroded, feeble, ferruginous, fiery,
   fire-red, flame-colored, flame-red, flaming, fossilized, foxy,
   fusty, gerontal, gerontic, glowing, gone to seed, grating, gules,
   henna, hoarse, hot, hot-tempered, ignorant, ill-humored,
   ill-natured, incarmined, inexperienced, infirm, inflamed, infrared,
   iron-red, jarring, lake-colored, laky, lateritious, liver-brown,
   liver-colored, livid-brown, lobster-red, lurid, mahogany, maroon,
   mildewed, moldering, moldy, moss-grown, mossbacked, moth-eaten,
   mummylike, musty, new to, on the downgrade, out of condition,
   out of shape, out of training, palsied, papery-skinned, port-wine,
   puce, rasping, raucous, ravaged with age, red, red-dyed,
   red-looking, reddened, reddish, reddish-amber, reddish-brown,
   rickety, roan, rough, rubicund, rubiginous, rubric, rubricose,
   ruby, ruby-colored, ruby-red, ruddied, ruddy, rufescent, rufous,
   rugged, ruined, ruinous, run to seed, russet, russety, rust,
   rust-cankered, rust-colored, rust-eaten, rust-red, rust-worn,
   scarlet, senile, shaky, shriveled, slipping, soft, stale, stammel,
   stiff, stricken in years, strident, sunburned, terra-cotta,
   tile-red, time-scarred, timeworn, tottering, tottery, unaccustomed,
   unacquainted with, unconversant with, unfamiliar with,
   unhabituated, unhardened, uninured, unpracticed, unseasoned,
   untrained, unused, unused to, unwonted, vermilion, vinaceous, warm,
   weak, weaned, wine, wine-colored, wine-red, withered, wizened,
   worn