brack·en (br?k??n)n.1. A fern (Pteridium aquilinum) found worldwide, with large, triangular fronds usually divided into three parts.2. An area with dense thickets of this fern.[Middle English braken, probably of Scandinavian origin; see bhreg- in Indo-European roots.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.bracken (?bræk?n) n1. (Plants) Also called: brake any of various large coarse ferns, esp Pteridium aquilinum, having large fronds with spore cases along the undersides and extensive underground stems2. (Plants) a clump of any of these ferns[C14: of Scandinavian origin; compare Swedish bräken, Danish bregne]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014brack?en (?bræk ?n) n. 1. a large fern, Pteridium aquilinum, of the polypody family, having large, creeping rootstocks and triangular fronds. 2. a cluster of such ferns. [1275?1325; Middle English braken