One of the mysteries of the English language finally explained.
In the genitive and attributive Designating a laboratory test used in the diagnosis of typhoid and other salmonella infections, based on the ability of the patient's serum to agglutinate a sample of the relevant bacteria; of or relating to this test.
Late 19th century; earliest use found in The Lancet. From the name of Georges Fernand Isidor Widal, French physician, who (with Arthur Sicard) described the test in 1896.
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