- A marble-sized ball, originally of camphor but now of naphthalene, stored with clothes to repel moths.
- A condition of long storage for possible future use: put the battleship into mothballs.
- A condition of being set aside or discarded: have put the plan into mothballs.
- To remove (a ship, for example) from active service or use and put into protective storage.
- To defer indefinitely; shelve: mothball a project.