The Collaborative International Dictionary of English v.0.48:

Depress \De*press"\, v. t. [imp. & p. p. Depressed; p. pr. &
   vb. n. Depressing.] [L. depressus, p. p. of deprimere; de-
   + premere to press. See Press.]
   1. To press down; to cause to sink; to let fall; to lower;
      as, to depress the muzzle of a gun; to depress the eyes.
      "With lips depressed." --Tennyson.
      [1913 Webster]

   2. To bring down or humble; to abase, as pride.
      [1913 Webster]

   3. To cast a gloom upon; to sadden; as, his spirits were
      depressed.
      [1913 Webster]

   4. To lessen the activity of; to make dull; embarrass, as
      trade, commerce, etc.
      [1913 Webster]

   5. To lessen in price; to cause to decline in value; to
      cheapen; to depreciate.
      [1913 Webster]

   6. (Math.) To reduce (an equation) in a lower degree.
      [1913 Webster]

   To depress the pole (Naut.), to cause the sidereal pole to
      appear lower or nearer the horizon, as by sailing toward
      the equator.

   Syn: To sink; lower; abase; cast down; deject; humble;
        degrade; dispirit; discourage.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Depressed \De*pressed"\, a.
   1. Pressed or forced down; lowed; sunk; dejected; dispirited;
      sad; humbled.
      [1913 Webster]

   2. (Bot.)
      (a) Concave on the upper side; -- said of a leaf whose
          disk is lower than the border.
      (b) Lying flat; -- said of a stem or leaf which lies close
          to the ground.
          [1913 Webster]

   3. (Zool.) Having the vertical diameter shorter than the
      horizontal or transverse; -- said of the bodies of
      animals, or of parts of the bodies.
      [1913 Webster]

WordNet (r) 3.0 (2006):

depressed
    adj 1: lower than previously; "the market is depressed"; "prices
           are down" [syn: depressed, down(p)]
    2: flattened downward as if pressed from above or flattened
       along the dorsal and ventral surfaces
    3: filled with melancholy and despondency ; "gloomy at the
       thought of what he had to face"; "gloomy predictions"; "a
       gloomy silence"; "took a grim view of the economy"; "the
       darkening mood"; "lonely and blue in a strange city";
       "depressed by the loss of his job"; "a dispirited and
       resigned expression on her face"; "downcast after his
       defeat"; "feeling discouraged and downhearted" [syn:
       gloomy, grim, blue, depressed, dispirited,
       down(p), downcast, downhearted, down in the mouth,
       low, low-spirited]

Moby Thesaurus II by Grady Ward, 1.0:

133 Moby Thesaurus words for "depressed":
   alveolar, alveolate, anguished, anxious, bad, badly off, blue,
   bored, bowed-down, cast down, cheerless, couchant, crouched,
   dashed, debased, dejected, dented, deprived, despairing,
   despondent, desponding, dimpled, dire, disadvantaged, disconsolate,
   discouraged, disgusted, disheartened, dispirited, donsie, doomful,
   down, downcast, downhearted, downthrown, drooping, droopy,
   engraved, evil-starred, fallen, fatal, faveolate, feeling low,
   flat, fortuneless, funest, grim, hapless, heartless, honeycombed,
   hypochondriac, hypochondriacal, ill off, ill-starred,
   in adverse circumstances, in low spirits, in the depths,
   in the doldrums, in the dumps, inauspicious, indented, joyless,
   knee-high, knocked flat, laid low, languishing, low, low-built,
   low-hung, low-level, low-leveled, low-lying, low-set, low-spirited,
   low-statured, lowered, luckless, lugubrious, melancholy, nauseated,
   nauseous, neap, notched, ominous, out of luck, pessimistic, pining,
   pitted, planet-struck, pleasureless, pocked, pockmarked,
   prey to malaise, prone, prostrate, recumbent, reduced, repelled,
   revolted, runty, sad, short, short of luck, sickened, spiritless,
   squat, squatty, star-crossed, stooped, stumpy, subdued, submerged,
   suffering angst, suicidal, sunk, sunken, supine, unblessed,
   underprivileged, uneasy, unelevated, unfortunate, unfulfilled,
   ungratified, unhappy, unlucky, unprosperous, unprovidential,
   unquiet, unsatisfied, weary of life, woebegone, world-weary