1. A woman who bears a child for another person, often for pay, either through artificial insemination or by carrying until birth another woman's surgically implanted fertilized egg: Recently on TV, there was a woman in California who was hired to be a surrogate mother for a Chinese couple.
2. One that acts as, serves as, or is a substitute mother: When little Tom's parents were killed in an automobile accident, his aunt who was taking care of him at the time became his surrogate mother.