Negligence, consisting in the omission of something which a party might do, and might reasonably be expected to do, towards the vindication or enforcement of his rights. The word is generally the synonym of “remissuess,” “dilatorlness,” “unreasonable or unexcused delay,” the opposite of “vigilance,” and means a want of activity and diligence in making a claim or moving for the enforcement of a right (particularly in equity) which will afford ground for presuming against it, or for refusing relief, where that is discretionary with the court.
LACHES
TheLaw.com Law Dictionary & Black's Law Dictionary 2nd Ed.