Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Mal- \Mal-\ (m[a^]l-). A prefix in composition denoting ill, or evil, F. male, adv., fr. malus, bad, ill. In some words it has the form male-, as in malediction, malevolent. See Malice.
Note: The form male- is chiefly used in cases where the e, either alone or with other letters, is pronounced as a separate syllable, as in malediction, malefactor, maleficent, etc. Where this is not the case, as in malfeasance or male-feasance, malformation or male-formation, etc., as also where the word to which it is prefixed commences with a vowel, as in maladministration, etc., the form mal is to be preferred, and is the one commonly employed.
Douglas Harper's Etymology Dictionary
word-forming element meaning "bad, badly, ill, poorly, wrong, wrongly," from French mal (adv.), from Old French mal (adj., adv.) "evil, ill, wrong, wrongly" (9c.), from Latin male (adv.) "badly," or malus (adj.) "bad, evil" (fem. mala, neuter malum), of unknown origin, perhaps related to Avestan mairiia "treacherous." Most Modern English words with this prefix are 19c. coinages.
Wiktionary
pre. 1 bad, badly as in maladjusted, malcontent - faulty, faultily as in malfunction 2 not