laches

{ } n. [ OF. lachesse, fr. lache lax, indolent, F. lâche, ultimately fr. L. laxus loose, lax. See Lax. ] (Law) Neglect; negligence; remissness; neglect to do a thing at the proper time; especially, a delay in asserting a claim, sufficient to cause a person to lose the right to adjuducation of the claim by a court. [ 1913 Webster ]

It ill became him to take advantage of such a laches with the eagerness of a shrewd attorney. Macaulay. [ 1913 Webster ]