-aceansuff.1. Variant of -aceous.2. An organism belonging to a taxonomic group: cetacean.[From New Latin -?cea, neuter pl. of -?ceus, -aceous.]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.