sur·ro·gate 
(sûrə-gĭt, -gāt′, sŭr-)
(sûrə-gĭt, -gāt′, sŭr-)n.
1. One that takes the place of another; a substitute.
2.
a. A person or animal that functions as a substitute for another, as in a social or family role.
b. A surrogate mother.
3. In Freudian psychology, a figure of authority who takes the place of the father or mother in a person's unconscious or emotional life.
4. Law A judge in New York and some other states having jurisdiction over the probate of wills and the settlement of estates.
adj.
Substitute.
tr.v. (-gāt′) sur·ro·gat·ed, sur·ro·gat·ing, sur·ro·gates
1. To put in the place of another, especially as a successor; replace.
2. To appoint (another) as a replacement for oneself.
[Middle English, from Latin surrogātus, past participle of surrogāre, to substitute, variant of subrogāre; see SUBROGATE.]