Vast means enormously wide and open, like an ocean or a desert. A vast area, vast sums, the vast majority.
It suits extent rather than height: a vast plain, not a vast tower. The vast majority is a very common fixed phrase and means almost all. Vastly is used before comparatives — vastly improved, vastly more expensive. Note that vast is not usually used of small things, however many of them there are, and that its Latin origin also meant empty, which is why it suits deserts so well.
1adjectivevastEnormously wide and open.
“The plain is vast and almost nothing grows on it.”
vast is a degree of size.
Also accepted in games: immense
Latin vastus meant both immense and desolate — the same word gave English waste and devastate. A vast place was originally an empty one, and the emptiness is still faintly in the word.
Latin
vastus — void, immense
Middle French
vaste
English, today
vast
From Middle French vaste, from Latin vastus (“void, immense”). Related to waste and German Wüste.
Etymology from Wiktionary, CC BY-SA