The verb oppress means to keep somebody down by using unjust force. For example, a cruel dictator might oppress his country’s people, or the ethnic majority of a population might oppress the minority. Oppress always has a negative connotation, and oppression is usually a continuous condition and not just a onetime event.
The word repress can be used in two ways:
1) To put a stop to something by force.
A country’s army can repress a revolution or revolt – stop it by fighting and winning against the revolutionaries. Politicians and governments can also repress opposition or dissent (disagreement) through control of the media as well as threatening people who have different opinions.
2) To hold back your feelings, or avoid revealing or acting on them.
If your boss makes an embarrassing mistake during a presentation to a client, you may have to repress your laughter (not laugh, even though you want to). The word “suppress” can also be used for this, and is probably more common.
In psychology, if feelings, memories, or desires are repressed, it means they are buried deep in the person’s consciousness (and often cause some negative effects on thinking or behavior). For example, a man who abuses children may have repressed memories of himself being abused when he was a child.
Suppress is the most common of the three, and has the most general meaning. It can be used:
1) In the same sense as repress – to stop a rebellion, uprising, revolt, or dissent by using force. Sometimes we add the adjectives violently, brutally, or bloodily if the suppression involved fighting and killing.
2) For holding back feelings – similarly to repress, but without the psychology meaning. If one of your co-workers who is extremely lazy receives a huge promotion, you might have to suppress your surprise upon hearing the news.
We often say somebody was “unable to suppress” their emotion if they couldn’t avoid showing their feelings, or “tried to suppress” their emotion if they are making an effort but having difficulty:
3) Prevent something from being revealed
A dishonest lawyer might suppress evidence in a criminal trial. A controlling government might suppress information or news that could present the government in a negative light.