When you're punctilious, you pay extremely careful attention to every tiny detail of correct behavior, proper procedures, or formal rules. A punctilious person follows protocols precisely and expects others to do the same.

A punctilious teacher marks exactly when students arrive, noting if they're even thirty seconds late. A punctilious dinner guest writes thank-you notes on proper stationery within exactly two days. A punctilious lawyer reviews every comma in a contract. These people aren't just careful: they're devoted to getting every small point exactly right according to the rules.

There's a difference between being meticulous (carefully thorough) and being punctilious (strictly proper about formal details). A meticulous scientist double-checks her measurements. A punctilious scientist insists the lab report must use Times New Roman font, size 12, with exactly one-inch margins, and refuses to read it otherwise.