Misfeasance

n. normally lawful act done in an unlawful way; misuse of authority; neglect of duty

The expressions misfeasance and nonfeasance, and occasionally malfeasance, are used in English law with reference to the discharge of public obligations existing by common law, custom or statute.Misfeasance is determined in relation to privity of contract. When a contract creates a duty that does not exist at common law, the parties can do one of three things: (1) perform the duty fully; (2) perform the duty inadequately or poorly; or (3) fail to perform the duty at all. When a party fails to perform at all, it is nonfeasance. When a party performs the duty inadequately or poorly, it is misfeasance. Malfeasance is used to denote outright sabotage which causes intentional damage.
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Noun
1. doing a proper act in a wrongful or injurious manner
(hypernym) wrongdoing, wrongful conduct, misconduct, actus reus

(n.)
A trespass; a wrong done; the improper doing of an act which a person might lawfully do.
  

Improperly doing something which a person has the legal right to do. Compare with malfeasance and nonfeasance. - (read more on Misfeasance)