Real Dictionary

mothball
countable noun: A mothball is a small ball made of a special chemical, which you can put among clothes or blankets in order to keep moths away.
verb: If someone in authority mothballs a plan, factory, or piece of equipment, they decide to stop developing or using it, perhaps temporarily.

mothball in American English
a small ball of naphthalene or, sometimes, camphor, the fumes of which repel moths, as from woolens, furs, etc.
in storage or reserve
to store with protective covering or set aside indefinitely for possible future use
noun: a small ball of naphthalene or sometimes of camphor for placing in closets or other storage areas to repel moths from clothing, blankets, etc

mothball in British English
noun: a small ball of camphor or naphthalene used to repel clothes moths in stored clothing, blankets, etc