his·tam·i·nase (h?-st?m??-n?s?, -n?z?, h?s?t?-m?-)n. An enzyme that catalyzes the inactivation of histamine and is found in the digestive system.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.histaminase (h??stæm??ne?s) n (Biochemistry) an enzyme, occurring in the digestive system, that inactivates histamine by removal of its amino group. Also called: diamine oxidase Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014his?tam?i?nase (h??stæm ??ne?s, -?ne?z) n. an enzyme that catalyzes the decomposition of histamine, used in treating allergies. [1925?30] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.