1. In aviation, a midair collision between two airplanes, thus resulting in a "shower" of debris from the sky. With so many more planes in the air these days, it's a wonder there aren't more aluminum showers.
2. obsolete An effort to collect household and scrap aluminum so as to aid in wartime production efforts. Primarily heard in US, South Africa. Officials pledged that the town would take part in an aluminum shower to replenish the raw resources that the arms industry so desperately needs.
3. obsolete A party, as for a bride-to-be, in which household items and appliances (i.e., those made of aluminum) are given as gifts. Primarily heard in US, South Africa. I was at a lovely aluminum shower for Jane last weekend. Someone even gave her an entire kitchen set!
See also: shower