salicylic acid: a white crystalline substance with a bitter aftertaste; used as a fungicide or in making aspirin or dyes or perfumes
hydroxy acid: any acid that has hydroxyl groups in addition to the hydroxyl group in the acid itself
sacrum: wedge-shaped bone consisting of five fused vertebrae forming the posterior part of the pelvis; its base connects with the lowest lumbar vertebra and its tip with the coccyx