The craft, business, or process of making or repairing barrels and wooden casks.
From 'cooper' + '-ing' suffix. The '-ing' suffix can form gerunds (noun forms of verbs) or present participles. In this case, it creates a noun meaning the activity or profession itself.
Coopering was so important that it was a seven-year apprenticeship—an aspiring cooper had to master complex geometry, woodworking, and metalworking to make watertight barrels that could withstand shipping and storage. It was medieval engineering.
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