To oppress is to treat someone cruelly or unjustly. Example:The child felt oppressed by the mean teacher.

To compress is to flatten, press, or squeeze an object. (Pronounced com-PRESS) Example: The machine compressed a symbol in to the metal. Also may be used to refer to medical bandaging to stop bleeding or inflammation. (Pronounced COM-press) Example: She used a compress to close the wound.

To repress is to restrain or prevent something. Example: I tried to repress the bad memory.

To suppress is to end something with force, or to prevent development. Example: The doctor suppressed the bleeding.