Dumb /dʌm/ As an adjective, it means stupid or unintelligent, but as slang, it functions as an adverb, meaning very. Examples: That exam was dumb hard! The journey to Budapest was dumb long. She is dumb tall.
Example: It's your birthday, Demi. Why the long face? Meaning: Why do you look so sad on your birthday? Synonymous: - Why are you sad? - Why are you unhappy? - Why are you upset?