-- action taken in an attempt to stop or penalise a person who makes a public statement or does something that is seen as a threat to a powerful interest group, such as a government, corporation or profession. Typical actions include ostracism, harassment, censorship, forced job transfer, reprimands and dismissal. Suppression is action against dissent that does not involve physical violence.
-- a person who engages in whistleblowing or, in other words, blows the whistle on wrongdoing; a dissenter from wrongdoing
Whistleblowers often are subject to suppression, but not always. Some individuals are subject to suppression even though they are not whistleblowers even in the loose sense. For example, individuals quietly adhering to unorthodox ideas may be subject to suppression.
-- violent action to oppose dissent, including beatings, imprisonment, torture and murder.
-- institutionalised lack of justice or freedom, such as poverty
maintained by exploitative social arrangements. Oppression is often
enforced by both suppression and repression.
These rather arbitrary distinctions between "suppression", "repression" and "oppression" are taken from Brian Martin, C. M. Ann Baker, Clyde Manwell and Cedric Pugh (eds.), Intellectual Suppression: Australian Case Histories, Analysis and Responses (Sydney: Angus and Robertson, 1986), pp. 1-3.
Brian Martin's website on suppression of dissent
in the section on Guide for newcomers