Merriam-Webster Collegiate Dictionary - surrogate motherhood

 noun see surrogate mother SURROGATE  I. transitive verb  (-gated; -gating)  Etymology: Latin surrogatus, past participle of surrogare to choose in place of another, substitute, from sub- + rogare to ask — more at right  Date: 1533 to put in the place of another:  a. to appoint as successor, deputy, or substitute for oneself  b. substitute  II. noun  Usage: often attributive  Date: 1603  1.  a. one appointed to act in place of another ; deputy  b. a local judicial officer in some states (as New York) who has jurisdiction over the probate of wills, the settlement of estates, and the appointment and supervision of guardians  2. one that serves as a substitute  3. ~ mother