Stiffly Proper is a term used to describe someone who is very formal and proper in their behavior. It is often used to describe someone who is very conservative and follows the rules of etiquette. The term is made up of two words, STAID and PRIM. STAID is an adjective meaning 'calm, sedate, and serious' while PRIM is an adjective meaning 'neat, precise, and proper'. Together, these two words create a phrase that describes someone who is very formal and proper in their behavior.