[or.ni.thine] n [ISV ornithuric acid (a compound of which ornithine is a component, found in the urine of birds) +
[2]-ine] (1881): a crystalline amino acid that functions esp. in urea production as a carrier by undergoing conversion to citrulline and then arginine in reaction with ammonia and carbon dioxide followed by recovery along with urea by enzymatic hydrolysis of arginine