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1. A Chilean evergreen tree (Quillaja saponaria) of the rose family, having bark used as soap and as a source of saponin.
2. The bark of this tree.
1. (Plants) Also called: quillai a W South American rosaceous tree, Quillaja saponaria, with undivided evergreen leaves and small white flowers
2. (Forestry) Also called: quillai bark the inner bark of this tree, formerly used as soap and as a source of saponin
3. (Plants) any of several trees or shrubs that have a bark similar to this