NMDA receptor (?n??m?d????)n. A brain receptor activated by glutamate, which when excessively stimulated may cause cognitive defects in Alzheimer’s disease.[N-m(ethyl)-d-a(spartate), an amino acid derivative that binds selectively to the receptor.]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.