When you retrieve something, you bring it back. Lots of dogs love to retrieve tennis balls, bringing them back to you over and over again.
You might retrieve your cell phone from the car, or the toys a baby throws repeatedly on the floor. You can also retrieve a memory from the recesses of your mind, or struggle to remember someone's name and then suddenly retrieve it. A retriever is a dog that's bred to bring things back — in fact, this is the word's earliest use, from the fifteenth century. The Old French root is retreuver, "find again," from re-, "again," and trouver, "to find."