"Once upon a midnight dreary, while I pondered, weak and weary" is the first line of Edgar Allen Poe's poem The Raven. Many a deep thinker has repeated it while musing. But if you've given up deep thinking, you may say instead, "Nevermore."
Think of ponder as reflecting on weighty thoughts. It will help you remember the definition if you can remember the word's Latin roots. It comes from ponderare, which literally meant to weigh, and pondus, which means weight. People sometimes use the word ironically, for example, when someone asks you to do something you really don't want to do. You may tap your chin for a second and say, "Let me ponder that." Pause. "Um, no!"