lin·seed (l?n?s?d?)n. The seed of flax, especially when used as the source of linseed oil; flaxseed.[Middle English linsed, from Old English l?ns?d : l?n, flax (from Latin l?num; see l??no- in Indo-European roots) + s?d, seed; see seed.]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.linseed (?l?n?si?d) n (Botany) another name for flaxseed[Old English l?ns?d, from l?n flax + s?d seed]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014flax?seed (?flæks?sid) n. the seed of flax; linseed. [1555?65] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.