/un ree"zeuhn/ , n.
1. inability or unwillingness to think or act rationally, reasonably, or sensibly; irrationality.
2. lack of reason or sanity; madness; confusion; disorder; chaos: a world torn by unreason.
v.t.
3. to upset or disrupt the reason or sanity of: The devious plot soon unreasoned the general.
[ 1250-1300; ME un-reson. See UN- 1 , REASON ]