Fastidiously proper NYT crossword clue

To be fastidiously proper means to exhibit extreme care in following rules or maintaining a particular standard of behavior. Individuals who are described this way tend to be meticulous, rigid, and sometimes overly formal in their actions and manners. Their behavior may appear overly strict or excessively neat, emphasizing correctness and propriety in all things.

The answer to this crossword clue is “PRIM.” A prim person is often seen as very proper, paying great attention to detail in both their actions and appearance. This term conveys someone who is fastidiously proper, always adhering to high standards of decorum and etiquette, sometimes to the point of being overly stiff or reserved.