to a great extent or degree
"I'm afraid the film was well over budget"
"painting the room white made it seem considerably (or substantially) larger"
"the house has fallen considerably in value"
"the price went up substantially"
Significantly; to a degree worth considering.
"The new policy has considerably improved employee morale across all departments."
In plain English: Considerably means by a large amount or to a significant degree.
"The new job pays considerably more than his previous position."
Usage: Use considerably to describe a significant or noticeable increase, decrease, or difference in amount or quality. It is often interchangeable with significantly but implies that the change is large enough to warrant attention rather than being merely minor.
Considerably comes from combining the word considerable with the suffix -ly. It entered English as an adverb to mean "to a significant degree."