malpractice

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Performance, as by a physician or lawyer, that falls below the professional minimum standard of care or service for a patient or client, especially when legally actionable because an injury or loss has been suffered by the patient or client.
• noun An instance of such performance.

from The Century Dictionary.

• noun Misbehavior; evil practice; practice contrary to established rules.
• noun Specifically, bad professional treatment of disease, pregnancy, or bodily injury, from reprehensible ignorance or carelessness, or with criminal intent.

from the GNU version of the Collaborative International Dictionary of English.

• noun Evil practice; illegal or immoral conduct; practice contrary to established rules; specifically, the treatment of a case by a surgeon or physician in a manner which is contrary to accepted rules and productive of unfavorable results.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun the improper treatment of a patient by a physician that results in injury or loss
• noun improper or unethical conduct by a professional or official person

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a wrongful act that the actor had no right to do; improper professional conduct
• noun professional wrongdoing that results in injury or damage