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.
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            For thee, oppress[`e]d king, am I cast down. --Shak.
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            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.
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WordNet (r) 3.0 (2006):

oppress
    v 1: come down on or keep down by unjust use of one's authority;
         "The government oppresses political activists" [syn:
         oppress, suppress, crush]
    2: cause to suffer; "Jews were persecuted in the former Soviet
       Union" [syn: persecute, oppress]