n 1  :  either of two isomeric cyclic crystalline compounds C₆H₄O₂ that are extremely irritating to the skin and mucous membranes  2  :  any of various usu. yellow, orange, or red quinonoid compounds including several that are biologically important as coenzymes, hydrogen acceptors, or vitamins .
 
   
 
Similar sounding terms:   canine  can·non  co·ni·ine  go·ni·on 
 
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