rock bottomn. The lowest possible level or absolute bottom: Prices have hit rock bottom.rock?-bot?tom 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.rock? bot?tom n. the very lowest level. [1865?70, Amer.] rock?-bot?tom adj. extremely low: rock-bottom prices. [1880?85] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.