The term 'EXTREMELY PROPER' can be broken down into two crossword solutions: PRIM (4 letters) and STRAIGHTLACED (13 letters). PRIM is an adjective that means 'very precise and formal in one's behavior or appearance'. STRAIGHTLACED is also an adjective that means 'very strict in one's behavior, especially in relation to moral standards'. Together, these two words describe someone who is extremely proper in their behavior and appearance.