'dreadfully' originates from the word 'dreadful,' which comes from the Old English word 'drēad,' meaning 'fear' or 'apprehension.'

'Drēad' transformed into the Middle English word 'dred,' and eventually became the modern English word 'dreadful,' with 'dreadfully' as its adverbial form.

Initially, it meant 'full of dread or fear,' but over time it evolved to also mean 'extremely' or 'very' in modern usage.