noun the powdered leaves, peduncles, and young branches of certain species of the sumac plant, used in tanning and dyeing.
2. sumach ·noun any plant of the genus rhus, shrubs or small trees with usually compound leaves and clusters of small flowers. some of the species are used in tanning, some in dyeing, and some in medicine. one, the japanese rhus vernicifera, yields the celebrated japan varnish, or lacquer.