The Collaborative International Dictionary of English v.0.48:

Aspirin \As"pi*rin\, n. (Pharm.)
   A white crystalline compound, acetyl salicylic acid
   (CH3.CO.O.C6H4.CO.OH) widely used as a drug for relief of
   pain and alleviation of fever. It has analgesic, antipyretic,
   and antiinflammatory properties, and is one of a class of
   agents called non-steroidal antiinflammatory drugs (NSAIDs).
   The name was originally a trade name, but has become the
   preferred name for the substance. It is actually a prodrug,
   liberating salicylic acid, the ultimate pharmacologically
   active agent, in the intestines. It is more effective when
   taken orally than is salicylic acid, because it dissolves
   more readily.

   Syn: 2-(acetyloxy)benzoic acid
        [Webster 1913 Suppl. +PJC]