The Collaborative International Dictionary of English v.0.48:

Undue \Un*due"\, a.
   1. Not due; not yet owing; as, an undue debt, note, or bond.
      [1913 Webster]

   2. Not right; not lawful or legal; improper; as, an undue
      proceeding. --Bacon.
      [1913 Webster]

   3. Not agreeable to a rule or standard, or to duty;
      disproportioned; excessive; immoderate; inordinate; as, an
      undue attachment to forms; an undue rigor in the execution
      of law.
      [1913 Webster]

   Undue influence (Law), any improper or wrongful constraint,
      machination, or urgency of persuasion, by which one's will
      is overcome and he is induced to do or forbear an act
      which he would not do, or would do, if left to act freely.
      --Abbott.
      [1913 Webster]