-aceous or -aceansuff.1. a. Of or relating to: amylaceous.b. Resembling or having the nature of: amentaceous.2. Belonging to a taxonomic group: orchidaceous.[From Latin -?ceus.]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.-aceous suffix forming adjectives relating to, belonging to, having the nature of, or resembling: herbaceous; larvaceous. [New Latin, from Latin -?ceus of a certain kind; related to -?c, -?x, adjectival suffix]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014-aceous a suffix with the meanings ?resembling, having the nature of,? ?made of,? occurring in loanwords from Latin (cretaceous; herbaceous) and forming adjectives in English on the Latin model, esp. adjectival correspondents to taxonomic names ending in -acea and -aceae: rosaceous. [