\Es*top"pel\, n. [From {Estop}.] (Law)
(a) A stop; an obstruction or bar to one's alleging or
    denying a fact contrary to his own previous action,
    allegation, or denial; an admission, by words or conduct,
    which induces another to purchase rights, against which
    the party making such admission can not take a position
    inconsistent with the admission.
(b) The agency by which the law excludes evidence to dispute
    certain admissions, which the policy of the law treats as
    indisputable. --Wharton. --Stephen. --Burrill.