n.
A condition in which symptoms of a mental disorder, such as the same delusional beliefs or ideas, occur simultaneously in two individuals who share a close relationship or association.
[French : folie, madness + à, between + deux, two.]
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.