Greatly means very much or to a large degree. It often describes strong feelings, big changes, or major differences.
“Greatly” is formed from “great” plus the adverb ending “-ly.” It has been used since Middle English to intensify the idea of size or importance.
‘Greatly’ sounds formal, so we use it more in writing than in casual speech, where we’d say ‘really’ or ‘a lot.’ English keeps multiple adverbs for the same idea, each with its own social ‘flavor.’
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