1. very large in extent or amount
the vast majority of people
As an adjective, 'vast' describes something extremely big or large in volume, size or extent. You might have a 'vast knowledge' of a topic, for example; or have 'vast experience' in a particular area. As a noun, 'vast' refers to a space that seems endless. 'Vast' can be used in both social and professional contexts and is similar in meaning to 'endless', 'considerable', 'extensive' or 'expansive'.