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.
   [1913 Webster]

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