Laches

Laches (Unreasonable Delay)

“[F]ailure to assert one’s rights in a timely manner can result in a claim being barred by laches.”
— Wikipedia

“Laches: An unreasonable delay pursuing a right or claim … in a way that prejudices the [opposing] party.”
— Black’s Law Dictionary, Ninth Edition

“[The artist] knew in 1981 what [the user] was publishing, what they were doing, and waited until 1987 to bring any action, and I do feel that that constitutes laches.”
— Silva v. MacLaine, 1988

“The person invoking laches is asserting that an opposing party has ‘slept on its rights,’ and that, as a result of this delay, circumstances have changed such that it is no longer just to grant the plaintiff’s original claim.”
— Wikipedia

“[T]he plaintiff comes ‘waltzing in at the eleventh hour’ when it is now too late to grant the relief sought, at least not without causing great harm that the plaintiff could have avoided.”
— Wikipedia

“[Laches] is generally allowed by a court when a defendant could reasonably have believed that the plaintiff was not going to exercise his or her legal rights and acted on that belief to his or her detriment.”
— Wikipedia

“Laches: A defense to an equitable action, that bars recovery by the plaintiff because of the plaintiff’s undue delay in seeking relief.”
— Legal Dictionary

Also see acquiescence.