Common Words:
* malady: a disease or illness
* malice: the desire to harm someone
* malignant: harmful or dangerous
* malnourished: lacking proper nourishment
* malpractice: improper or negligent professional treatment
* maltreat: to treat badly or cruelly
* malware: software designed to damage or disable a computer system
Less Common Words:
* malaise: a general feeling of discomfort, illness, or uneasiness
* malapropism: the humorous misuse of a word, especially by substituting a word with a similar sound
* malcontent: a person who is dissatisfied with the current situation
* malfeasance: misconduct or wrongdoing by a public official
* mallard: a type of wild duck
* malodorous: having a bad smell
* malversation: dishonest or illegal conduct by someone in a position of trust
* maladjusted: poorly adjusted to the environment or society
* malapropos: inappropriate or untimely
* malarkey: nonsense or foolishness
This list is not exhaustive, but it gives you a good starting point for words beginning with "mal".