flaxLinum usitatissimumflax (fl?ks)n.1. a. A widely cultivated plant, Linum usitatissimum, having pale blue flowers, seeds that yield linseed oil, and slender stems from which a textile fiber is obtained.b. The fine, light-colored textile fiber obtained from this plant.c. Any of various other plants of the genus Linum or of other genera in the family Linaceae.2. A pale grayish yellow.[Middle English, from Old English fleax; see plek- in Indo-European roots.]flax?y adj.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.