WordNet (r) 3.0 (2006):

cy pres
    n 1: a rule that when literal compliance is impossible the
         intention of a donor or testator should be carried out as
         nearly as possible [syn: cy pres, rule of cy pres, cy
         pres doctrine]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CY PRES, construction. These are old French words, which signify "as near
as."
     2. In cases where a perpetuity is attempted in a will, the courts do
not, if they can avoid it, construe the devise to be utterly void, but
expound the will in such a manner as to carry the testator's intentions into
effect, as far as the rules respecting perpetuities will allow; this is
called construction cy pres. When the perpetuity is attempted in a deed, all
the limitations are totally void. Cruise, Dig. t. 38, c. 9, s. 34; and vide
1 Vern. 250; 2 Ves. Jr. 380, 336, 357, 364; 3 Ves. Jr. 141, 220; 4 Ves. 13;
Com. Dig. Condition, L. 1; 1 Rop. Leg. 514; Swinb. pt. 4, s. 7, a. 4; Dane's
Ab. Index, h.t.; Toull. Dr. Civ. Fr. liv. 3, t. 3, n. 586, 595, 611; Domat,
Loix Civ. liv. 6. t. 2, s. 1; 1 Supp. to Ves. Jr. 134, 259, 317; 2 Id.
316,473; Boyle on Charities, Index, h.t.; Shelford on Mortmain, Index, h.t.;
3 Bro. C. C. 166; 2 Bro. C. C. 492; 4 Wheat. R. 1; S. C. 3 Peters, R. App.
481; 3 Peters, R. 99; 15 Ves., 232; 2 Sto. Eq. Jur. Sec. 1169.