Extremely is the word you reach for when 'very' is not strong enough. Extremely cold, extremely tired, extremely careful with the good glasses.
It stands in front of adjectives and adverbs, never in front of a noun and never with a verb on its own: you can be extremely angry, but you cannot 'extremely want' something. Keep it away from adjectives that are already absolute — extremely perfect and extremely dead add nothing that perfect and dead had not already said. It belongs to the family of extreme, extremist and extremity, and it is at home in careful writing as well as in speech: an extremely rare condition, an extremely narrow margin. Because it is strong, it wears out fast; a page where everything is extremely something reads as though nothing is.
1adverbextremelyTo a very great degree; more than very.
“The exam was extremely difficult, and half the class ran out of time.”
synonyms: exceedingly, highly, intensely
Latin
extrēmus
Old French
extreme
English
extreme
English, today
extremely
From extreme + -ly. extreme Borrowed into late Middle English - from Old French extreme, from Latin extrēmus, the superlative of exter.
Etymology from Wiktionary, CC BY-SA