In storage, either literally or figuratively. Mothballs—little balls composed of a pungent chemical used to deter moths—are often kept in closets, attics, and other places where clothes are stored. I'm so glad that I can finally get my summer clothes out and put my winter clothes back in mothballs.That plane is in mothballs while we wait for a new shipment of parts.I did like your idea, Tom, but we have to keep it in mothballs for now while we finish our outstanding projects.