The Collaborative International Dictionary of English v.0.48:
Laches \Lach"es\ (l[a^]sh"[e^]z), Lache \Lache\ (l[a^]sh), n.
[OF. lachesse, fr. lache lax, indolent, F. l[^a]che,
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.
It ill became him to take advantage of such a laches
with the eagerness of a shrewd attorney. --Macaulay.