plural noun (sometimes initial capital letter)

long, full sideburns or muttonchop whiskers.

Origin of dundrearies

1860–65; after the sideburns worn by actor Edward A. Sothern as Lord Dundreary, a character in the play Our American Cousin (1858) by Tom Taylor
Also called dun·drear·y whisk·ers.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for dundrearies

1867, long, flowing whiskers, like those worn by actor E.A. Sothern (1826-1881) while playing Lord Dundreary, witless, indolent chief character in English dramatist Tom Taylor's play "Our American Cousin" (1858).

Online Etymology Dictionary, © 2010 Douglas Harper