Rapidly means at great speed. Growing rapidly, rapidly changing, deteriorate rapidly.
It goes with change above all — rapidly rising, rapidly falling, a rapidly changing situation — and far less often with plain movement, where quickly does the work. In medicine, deteriorating rapidly is a phrase nobody wants to hear.
1adverbrapidlyAt great speed.
“The fire spread rapidly through the dry forest.”
rapidly is a speed.
Latin
rapidus
Middle French
rapide
English
rapid
English, today
rapidly
From rapid + -ly. rapid Borrowed from Middle French rapide, from Latin rapidus. Borrowed from Middle French rapide and its etymon Latin rapidus.
Etymology from Wiktionary, CC BY-SA