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.
2. Not right; not lawful or legal; improper; as, an undue
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
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.