
One of the fastest ways to increase your vocabulary is by learning word parts, i.e., roots, prefixes, suffixes or forms.
mal - bad
malignant - cause harm or damage; malinger - pretend to be sick so you don't have to go to work; malapropism - saying something wrong or have it come out funny; maladroit - clumsy, bad coordination; malaise - discomfort, not feeling well; mal de mer - bad from the ocean, sea sickness.
Here's some others:
malnutrition, malady, malodorous, malpractice, malice, malevolent, malefactor, malicious, malign, malediction, malapropos.