fis·sure (f?sh??r)n.1. A long narrow opening; a crack or cleft.2. The process of splitting or separating; division.3. A separation into subgroups or factions; a schism.4. Anatomy A normal groove or furrow, as in the liver or brain, that divides an organ into lobes or parts.5. Medicine A break in the skin, usually where it joins a mucous membrane, producing a cracklike sore or ulcer.intr. & tr.v. fis·sured, fis·sur·ing, fis·sures To form a crack or cleft or cause a crack or cleft in.[Middle English, cut, from Old French, from Latin fiss?ra, from fissus, split; see fissi-.]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.fissure (?f???) n1. any long narrow cleft or crack, esp in a rock2. a weakness or flaw indicating impending disruption or discord: fissures in a decaying empire. 3. (Anatomy) anatomy a narrow split or groove that divides an organ such as the brain, lung, or liver into lobes. See also sulcus4. (Medicine) a small unnatural crack in the skin or mucous membrane, as between the toes or at the anus5. (Dentistry) a minute crack in the surface of a tooth, caused by imperfect joining of enamel during developmentvbto crack or split apart[C14: from medical Latin fiss?ra, from Latin fissus split]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014fis?sure (?f?? ?r) n., v. -sured, -sur?ing. n. 1. a narrow opening produced by cleavage or separation of parts. 2. cleavage (def. 2). 3. a natural division or groove in an anatomical organ, as in the brain. v.t. 4. to make fissures in; cleave; split. v.i. 5. to open in fissures; become split. [1375?1425; late Middle English