n.
Any of a variety of substances, including certain vitamins, herbs, and prescription drugs, reputed to improve such mental functions as memory and alertness or to lessen or prevent damage to brain cells.
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
