krill (kr?l)n. pl. krill The collection of small marine crustaceans of the order Euphausiacea that are the principal food of baleen whales.[Norwegian kril, young fry of fish.]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.krill (kr?l) n, pl krill (Animals) any small shrimplike marine crustacean of the order Euphausiacea: the principal food of whalebone whales[C20: from Norwegian kril young fish]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014krill (kr?l) n., pl. krill. any of the small, pelagic, shrimplike crustaceans of the family Euphausiidae. [1905?10;