vastly
adv.to a very great degree. You use this when you want to emphasize that a difference or change is very large.
adv.to a very great extent or degree; immensely. Frequently modifies adjectives or verbs to emphasize a significant disparity or improvement.
“The new model is vastly better than the old one.”
“The quality of life in the city has improved vastly since the new public transport system was built.”
“While the two theories share a common origin, their modern applications have diverged vastly, leading to entirely different conclusions in the field of quantum mechanics.”
Typically placed before the adjective it modifies or after the verb it emphasizes.
Learners sometimes use the adverb 'vastly' when the sentence requires the adjective 'vast' to describe a noun.
Usage vastly different
“The hot tea is clearly at a much higher temperature than the iceberg, but the large iceberg has vastly more energy than the tiny cup of tea.”
“These were two vastly different worlds, connected by one strange little bird: the marbled murrelet.”
From vast + -ly.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.