If you're a cunctator, you tend to procrastinate, or put off til later what you should probably do right now. Your teacher might call you a cunctator if you start writing your paper the night before it's due.
A cunctator has a habit of postponing or delaying action, often out of laziness. When you come across this unusual word, it's very often capitalized — in this case, it refers specifically to the Roman statesman Fabius Maximus, who became well-known for his cautious military strategy against the Carthaginians during the Second Punic War in the 200s BCE. He was called the Cuncator, Latin for "delayer."