I need a single-word for the meaning of "abuse of the authoritative/political power".
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As Mehper suggests, malfeasance is very probably the word you're looking for, but since we know the abuse of political power takes a multitude of varied and awful forms you could use a more descriptive word depending on the nature and consequence of the corruption you have in the spotlight.
For instance we have fraud, extortion, blackmail, bribery, deception, betrayal, torture, greed, prejudice, laziness, apathy. All the seven deadly sins and many more.
The abuse of political power and the underlying moral degeneracy should not be obscured by dry and detached words unless you're aiming for an ironic tone or want to obscure the degeneracy with weasel words.
If you really want to generalise then try a word like scrofulous, which has at least an association with a horrible disease.
It would be helpful to have the context in which this word is needed, but you could try despotism, autocracy, fascism, tyranny, totalitarianism, or oligarchy.
Tyranny has the stylistic and emotive impact I suspect suits the context you have in mind.
You kind of either have petty larcency or ruthless tyranny. Though everyone in power abuses power, very few are true tyrants. Most are merely motivated by petty greed.