adj. 1.  Of or relating to chemistry. 2.  Of or relating to the properties or actions of chemicals. 3.  Of or relating to chemical weapons: chemical warfare. n. 1.  A substance with a distinct molecular composition that is produced by or used in a chemical process. 2.  A drug, especially an illicit or addictive one. [Obsolete chimical, from chimic, alchemist, from New Latin chimicus, from Medieval Latin alchimicus, from alchymia, alchemy; see  ALCHEMY.] chemi·cal·ly adv.  | 
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