The Collaborative International Dictionary of English v.0.48:

overcast \o`ver*cast"\, a.
   1. (Meteorology) Completely or almost completely covered over
      with clouds; -- of the sky.
      [PJC]

   2. (Sewing) Sewn by overcasting.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Overcast \O`ver*cast"\ ([=o]`v[~e]r*k[.a]st"), v. t.
   1. To cast or cover over; hence, to cloud; to darken.
      [1913 Webster]

            Those clouds that overcast your morn shall fly.
                                                  --Dryden.
      [1913 Webster]

   2. To compute or rate too high. --Bacon.
      [1913 Webster]

   3. (Sewing) To take long, loose stitches over (the raw edges
      of a seam) to prevent raveling.
      [1913 Webster]

   4. (Bookbinding) To fasten, as single sheets, by overcast
      stitching or by folding one edge over another.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

overcast
    adj 1: filled or abounding with clouds [syn: cloud-covered,
           clouded, overcast, sunless]
    n 1: the state of the sky when it is covered by clouds [syn:
         cloudiness, cloud cover, overcast]
    2: gloomy semidarkness caused by cloud cover [syn: cloudiness,
       overcast]
    3: a long whipstitch or overhand stitch overlying an edge to
       prevent raveling [syn: overcast, overcasting]
    4: a cast that falls beyond the intended spot
    v 1: make overcast or cloudy; "Fall weather often overcasts our
         beaches" [syn: overcast, cloud] [ant: brighten,
         clear, clear up, light up]
    2: sew over the edge of with long slanting wide stitches
    3: sew with an overcast stitch from one section to the next;
       "overcast books"

Moby Thesaurus II by Grady Ward, 1.0:

158 Moby Thesaurus words for "overcast":
   Acheronian, Acherontic, CAT, Cimmerian, Stygian, adumbrate,
   aerospace, aerosphere, air hole, air pocket, airspace, becloud,
   bedarken, bedim, befog, begloom, bemist, black, black out, blacken,
   blackening, blanket, block the light, blocking the light, blot out,
   brooding, brown, bump, cap, cast a shadow, castellatus, ceiling,
   cirrose, cirrous, clabber up, cloud, cloud over, cloud up,
   cloud-flecked, clouded, cloudiness, clouding, cloudy, crosswind,
   crown, cumuliform, cumulous, dark, dark and gloomy, darken,
   darken over, darkened, darkening, dim, dim out, dimming, dirty,
   dirty sky, dismal, dreary, dull, eclipse, eclipsing, empty space,
   encloud, encompass with shadow, enmist, extinguishment,
   favorable wind, fog, fogginess, front, funereal, gloom, gloomful,
   glooming, gloomy, grey, haze, haziness, head wind, heavy,
   heavy sky, high-pressure area, hole, ill-lighted, ill-lit,
   ionosphere, jetstream, lenticularis, low-pressure area, lowering,
   mammatus, menacing, mist, mistiness, murk, murky, nebulosity,
   nebulous, nimbose, nimbosity, nubilate, nubilation, nubilous,
   obfuscate, obfuscation, obnubilate, obnubilation, obscuration,
   obscure, obscurement, obumbrate, obumbration, occult, occultate,
   occulting, oppressive, overcloud, overclouded, overclouding,
   overlay, overshading, overshadow, overshadowing, overshadowment,
   oversmoke, overspread, pocket, roughness, shade, shading, shadow,
   shadowing, smog, smoke, somber, sombrous, soup, space, squally,
   starless, stormy, stratiform, stratosphere, stratous,
   substratosphere, sullen, sunless, tail wind, threatening,
   thunderheaded, tropopause, troposphere, trough, turbulence,
   visibility, visibility zero