Stumble upon Definition 1 of 2Pro Tip 1/3Unplanned Discovery Used when finding something good or interesting without looking for it. I stumbled upon a charming little cafe while exploring the town. Pro Tip 2/3Positive Surprise Often carries a positive connotation, as if luck brought you to a pleasant find. She stumbled upon a rare book at a garage sale. Pro Tip 3/3Casual Tone Common in casual conversation, not usually used in formal writing. Guess what? I stumbled upon your favorite candy at the store.