n 1  :  a product of metabolism:  a  :  a metabolic waste usu. more or less toxic to the organism producing it  :  EXCRETION  b  :  a product of one metabolic process that is essential to another such process in the same organism  c  :  a metabolic waste of one organism that is markedly toxic to another  :  ANTIBIOTIC  2  :  a substance essential to the metabolism of a particular organism or to a particular metabolic process .
 
 
 
Similar sounding terms:  mu·ta·bil·i·ty 
 
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