rock houndn. Informal 1. One who specializes in geology.2. One who collects rocks and minerals, especially gemstones, as a hobby.rock? hound?ing, rock?hound?ing (r?k?houn?d?ng) n.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? hound` or rock?hound`, n. an amateur collector of rocks and minerals. [1920?25, Amer.] rock? hound`ing, n. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.