say it: VAST-lee
vastly is an adverb meaning "to an exceedingly great extent or degree". It is pronounced /ˈvæstli/ — VAST-lee. It carries one recorded sense.
to an exceedingly great extent or degree
“He had vastly overestimated his resources”
“was immensely more important to the project as a scientist than as an administrator”
Definitions, synonyms and semantic relations for vastly come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.