to dominate harshly and unfairly (as in "oppressive government")
to deny equal rights to others or make them suffer (as in "The government oppresses minorities.")
…del Toboso, fairest of the fair! since it has fallen to thy lot to hold subject and submissive to thy full will and pleasure a knight so renowned as is and will be Don Quixote of La Mancha, who, as all the world knows, yesterday received the order of knighthood, and hath to-day righted the greatest wrong and grievance that ever injustice conceived and cruelty perpetrated: who hath to-day plucked the rod from the hand of yonder ruthless oppressor so wantonly lashing that tender child.
…whom it would have been better not to have been so ready to believe lovers’ promises, which are for the most part quickly made and very slowly performed; and so, with my lord the duke’s leave, I will at once go in quest of this inhuman youth, and will find him out and challenge him and slay him, if so be he refuses to keep his promised word; for the chief object of my profession is to spare the humble and chastise the proud; I mean, to help the distressed and destroy the oppressors."
There are no more uses of "oppress" identified with this meaning, but check unspecified meaning below.
If thy beauty despises me, if thy worth is not for me, if thy scorn is my affliction, though I be sufficiently long-suffering, hardly shall I endure this anxiety, which, besides being oppressive, is protracted.
All which presents itself now to my mind, urging, persuading, and even compelling me to demonstrate in your case the purpose for which Heaven sent me into the world and caused me to make profession of the order of chivalry to which I belong, and the vow I took therein to give aid to those in need and under the oppression of the strong.
…all who had been present at the burial of Chrysostom, he and his squire passed into the same wood which they had seen the shepherdess Marcela enter, and after having wandered for more than two hours in all directions in search of her without finding her, they came to a halt in a glade covered with tender grass, beside which ran a pleasant cool stream that invited and compelled them to pass there the hours of the noontide heat, which by this time was beginning to come on oppressively.
…your dress would hide, senora, is made known to us by your hair; a clear proof that it can be no trifling cause that has disguised your beauty in a garb so unworthy of it, and sent it into solitudes like these where we have had the good fortune to find you, if not to relieve your distress, at least to offer you comfort; for no distress, so long as life lasts, can be so oppressive or reach such a height as to make the sufferer refuse to listen to comfort offered with good intention.
And yet, with all these good things, which are commonly all that men need to enable them to live happily, I am the most discontented and dissatisfied man in the whole world; for, I know not how long since, I have been harassed and oppressed by a desire so strange and so unusual, that I wonder at myself and blame and chide myself when I am alone, and strive to stifle it and hide it from my own thoughts, and with no better success than if I were endeavouring deliberately to publish it to…
"Blockhead!" said Don Quixote at this, "it is no business or concern of knights-errant to inquire whether any persons in affliction, in chains, or oppressed that they may meet on the high roads go that way and suffer as they do because of their faults or because of their misfortunes.