—adj. 1. of very great area or extent; immense: the vast reaches of outer space. 2. of very great size or proportions; huge; enormous: vast piles of rubble left in the wake of the war. 3. very great in number, quantity, amount, etc.: vast sums of money. 4. very great in degree, intensity, etc.: an artisan of vast skill.
—n. Literary.an immense or boundless expanse or space.