aspirin: the acetylated derivative of salicylic acid; used as an analgesic anti-inflammatory drug (trade names Bayer, Empirin, and St. Joseph) usually taken in tablet form; used as an antipyretic; slows clotting of the blood by poisoning platelets
substance: the real physical matter of which a person or thing consists
muskrat: beaver-like aquatic rodent of North America with dark glossy brown fur