surrogate (n.)

early 15c., from Latin surrogatus, past participle of surrogare/subrogare "put in another's place, substitute," from assimilated form of sub "in the place of, under" (see sub-) + rogare "to ask, propose," apparently a figurative use of a PIE verb meaning literally "to stretch out (the hand)," from root *reg- "move in a straight line." Meaning "woman pregnant with the fertilized egg of another woman" is attested from 1978 (from 1972 of animals; surrogate mother in a psychological sense is from 1971). As an adjective from 1630s.

updated on April 28, 2017

Definitions of surrogate from WordNet
surrogate (n.)
someone who takes the place of another person;
Synonyms: alternate / replacement
surrogate (n.)
a person appointed to represent or act on behalf of others;
Synonyms: deputy
surrogate (adj.)
providing or receiving nurture or parental care though not related by blood or legal ties;
surrogate father
Synonyms: foster
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