Definition of "lactase" []

• An enzyme occurring in certain yeasts and in the intestinal juices of mammals and catalyzing the hydrolysis of lactose into glucose and galactose. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Those with celiac disease often become lactose intolerant because the disease affects the inner lining of the intestine where lactase is made."
• "Usually lactose intolerant means that the enzyme lactase is missing or in small quantities."
• "(Lactose intolerance has proven intractable because the lack of lactase is not reversible.)"