Sideburns are whiskers that are worn on the sides of a man’s face, especially when the beard on the chin is shaved. The term is an alteration of the name of General A.E. Burnside (1824-81), a Union general in the US Civil War more famed for his whiskers than his abilities on the battlefield.
The term burnsides, referring to a style of whiskers worn by the general, occurs as early as 1875. From the Cincinnati Enquirer of 6 July of that year:
His whisker was of the Burnside type, consisting of mustache and “muttonchop,” the chin being perfectly clean.
Within a decade or so of the appearance of burnside, the order of the syllables was reversed. Presumably, as memories of the Civil War and the name Burnside faded, folk etymology took over and tried to make sense of the term by emphasizing the side.
From the Chicago Journal of 1 August 1887:
McGarigle has his mustache and small sideburns still on.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2017, by David Wilton