delusion , illusion : Discriminate carefully between these terms. A delusion is a mental error arising from false views or an unbalanced state of mind; an illusion is an unreal image which is presented to the senses. A mirage is an optical illusion.

n. The father of a most respectable family, comprising Enthusiasm, Affection, Self-denial, Faith, Hope, Charity and many other goodly sons and daughters.

  All hail, Delusion!  Were it not for thee
  The world turned topsy-turvy we should see;
  For Vice, respectable with cleanly fancies,
  Would fly abandoned Virtue's gross advances.

Mumfrey Mappel