bra·chi·o·sau·rus (br??k?-?-sôr??s, br?k??-)n. A large brachiosaurid dinosaur of the genus Brachiosaurus of the Jurassic Period, with the nostrils and eyes set high up on the head. Also called brachiosaur.[New Latin Br?chiosaurus, genus name : Latin br?cchium, arm; see brachium + Greek sauros, lizard.]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.brachiosaurus (?bre?k???s??r?s; ?bræk-) n (Animals) a dinosaur of the genus Brachiosaurus, up to 30 metres long: the largest land animal ever known. See also sauropodCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014bra·chi·o·sau·rus (br??k?-?-sôr??s) or bra·chi·o·saur (br??k?-?-sôr?) Plural brachiosauri or brachiosaurs A massive sauropod dinosaur of the Jurassic and Cretaceous Periods. It had forelegs that were longer than its hind legs, and nostrils on top of its head.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.