Is it ensure, insure, or assure?
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.
Bad; badly: malpractice.
Abnormal; abnormally: malformation.