Synonyms for Surrogate (same or very similar meaning)
WordNet sense 1 (someone who takes the place of another person):
alternate, replacement, alternate
WordNet sense 2 (a person appointed to represent or act on behalf of others):
deputy
WordNet sense 3 (providing or receiving nurture or parental care though not related by blood or legal ties):
foster
WordNet sense 4 (of parents and children; related by adoption):
adoptive
From the ODE community, based on WordNet
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