The term 'rust bucket' is a slang term used to describe an old, dilapidated vehicle. The crossword solutions for this term are HEAP (4 letters), CRATE (5 letters), and TUB (3 letters). A HEAP is a large pile of something, usually disorganized. A CRATE is a box or container, often made of wood, used for storage or transport. A TUB is a large, open-topped container, usually made of metal or plastic, used for storing or transporting liquids or other materials. All three of these words can be used to describe an old, run-down vehicle, which is why they are all valid solutions for the term 'rust bucket'.