to oppress or wrong someone weaker: to treat a person harshly and unjustly, especially one who has no power to resist
At its heart this word is about the abuse of an advantage. Whenever someone with the upper hand, a landowner, a ruler, a buyer, or a conquering army, uses that power to harm someone who cannot push back, this is the verb the Bible reaches for. That is why it appears so often in Israel's law protecting the foreigner, the widow, the orphan, and the poor: these are exactly the people with no leverage of their own.
The same act wears different clothes depending on the setting. In daily life it is mistreating the defenseless outright. In the marketplace it is the quieter cruelty of cheating a neighbor on a price. On the national stage it becomes the oppressor as a figure, whether the sword, the proud nation, or the city that lives by crushing others. The word holds these together because they are one thing seen from different angles: the strong bending the weak to their will.
A closely related word, עָשַׁק, narrows in on extortion and holding back what someone is owed, and לָחַץ pictures the squeezing pressure an oppressor applies. This word stays broader, naming the wrong itself rather than one form of it.