Extremely
Part of speech: adverb
Definition: To an extreme degree.
Example sentence: Be extremely subtle, even to the point of formlessness. Be extremely mysterious, even to the point of soundlessness. Thereby you can be the director of the opponent's fate.
Highly
Part of speech: adverb
Definition: In a high or esteemed manner.extremely; greatly; awfully
Example sentence: A highly developed stock exchange cannot be a club for the cult of ethics.