To cadge is to plead or beg for something. A hungry child might cadge an extra cookie from her dad while he's baking.
When you cadge something, you wheedle or plead for it, manipulating someone into giving it to you. If you forget your lunch, you might have to cadge parts of your friend's meal, and if you don't have change for a parking meter, you might try to cadge some from a person walking by. Since the early 1800s, to cadge has meant "to beg," and while its origin is uncertain, it may come from cadger, "itinerant dealer" or "peddler."