What's the difference between 굉장히 크다 and 굉장히 작다.

 ANSWER: One makes sense and the other doesn't.

매우 크다 means "very big," and 매우 작다 means "very small," but even though one can use 굉장히 크가 to mean, "very big," one cannot use 굉장히 작다 to mean, "very small." Why not?

Because 굉장히 is normally used in colloquial speech to describe big or magnificent things, not small or petty things. Also, it is normally used to describe positive things rather than negative things, so, "굉장히 좋다" (very good) makes more sense than "굉장히 나쁘다" (very bad).