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.
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   2. To bring down or humble; to abase, as pride.
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   3. To cast a gloom upon; to sadden; as, his spirits were
      depressed.
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   4. To lessen the activity of; to make dull; embarrass, as
      trade, commerce, etc.
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   5. To lessen in price; to cause to decline in value; to
      cheapen; to depreciate.
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   6. (Math.) To reduce (an equation) in a lower degree.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Depress \De*press"\, a. [L. depressus, p. p.]
   Having the middle lower than the border; concave. [Obs.]
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         If the seal be depress or hollow.        --Hammond.
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WordNet (r) 3.0 (2006):

depress
    v 1: lower someone's spirits; make downhearted; "These news
         depressed her"; "The bad state of her child's health
         demoralizes her" [syn: depress, deject, cast down,
         get down, dismay, dispirit, demoralize,
         demoralise] [ant: elate, intoxicate, lift up, pick
         up, uplift]
    2: lower (prices or markets); "The glut of oil depressed gas
       prices"
    3: cause to drop or sink; "The lack of rain had depressed the
       water level in the reservoir" [syn: lower, depress]
    4: press down; "Depress the space key" [syn: press down,
       depress]
    5: lessen the activity or force of; "The rising inflation
       depressed the economy"

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "depress":
   abridge, bear down, beat down, bring down, bring low, burden,
   cast down, cheapen, compress, couch, countersink, curtail, cut,
   cut back, cut down, damp, dampen, dampen the spirits, darken, dash,
   debase, debilitate, decrease, deduct, deepen, deflate, deject,
   demit, dent, depreciate, detrude, devaluate, devalue, dig,
   diminish, dimple, dint, discourage, dishearten, dispirit, dive,
   downbear, downgrade, drill, droop, dull, enervate, engrave,
   excavate, grieve, haul down, impress, imprint, indent, knock down,
   lessen, let, let down, lower, lower the spirits, mine, notch,
   oppress, pare, pit, pock, pockmark, press down, press in,
   pull down, punch, punch in, push down, recess, reduce, retrench,
   roll back, sadden, sap, scale down, set back, set in, shorten,
   simplify, sink, stamp, step down, take down, take from, tamp,
   thrust down, tune down, tunnel, upset, weaken, weigh down,
   weigh heavy upon, weigh upon