Other forms: heftier; heftiest; heftily
Something that's hefty is big and heavy. When you have to lug a hefty suitcase around, it helps if it has wheels.
Hefty objects are large and bulky, and you can describe people as hefty when they're big and brawny and strong. When you buy a hefty bag of dog food for your hefty bull mastiff, you might want to ask a hefty young employee if she'll help you carry it to your car. Hefty comes from heft, which means both "to lift" and "weight or heaviness."