Laches
Laches (lash"ez) , noun
[Old French lachesse, from lache lax, indolent, French lâche, ultimately from Latin 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.
It ill became him to take advantage of such a laches with the eagerness of a shrewd attorney.
Also: Lache