Aq·ua-Lung (?k?w?-l?ng?, ä?kw?-) A trademark for an underwater breathing apparatus.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.Aq?ua-lung` (?æk w?, ?? kw?) Trademark. a brand of scuba apparatus. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.