The Collaborative International Dictionary of English v.0.48:

Oppress \Op*press"\, v. t. [imp. & p. p. Oppressed; p. pr. &
   vb. n. Oppressing.] [F. oppresser, LL. oppressare, fr. L.
   oppressus, p. p. of opprimere; ob (see Ob-) + premere to
   press. See Press.]
   1. To impose excessive burdens upon; to overload; hence, to
      treat with unjust rigor or with cruelty. --Wyclif.
      [1913 Webster]

            For thee, oppress[`e]d king, am I cast down. --Shak.
      [1913 Webster]

            Behold the kings of the earth; how they oppress
            Thy chosen!                           --Milton.
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   2. To ravish; to violate. [Obs.] --Chaucer.
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   3. To put down; to crush out; to suppress. [Obs.]
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            The mutiny he there hastes to oppress. --Shak.
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   4. To produce a sensation of weight in (some part of the
      body); as, my lungs are oppressed by the damp air; excess
      of food oppresses the stomach.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

oppressed \oppressed\ adj.
   having excessive or unfair burdens imposed.

   Syn: downtrodden, persecuted.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

oppressed
    adj 1: burdened psychologically or mentally; "laden with grief";
           "oppressed by a sense of failure" [syn: laden,
           oppressed]