crab lousen. A parasitic louse (Phthirus pubis) that infests the pubic region and causes severe itching. Also called pubic louse.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.crab louse n (Animals) a parasitic louse, Pthirus (or Phthirus) pubis, that infests the pubic region in humans Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014crab? louse` n. a crablike louse, Phthirus pubis, that infests pubic hair and other body hair in humans. [1540?50] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.