a person appointed to act in place of another; a substitute or deputy
a deputy appointed to act for a bishop in granting marriage licences
a local judicial officer in some states of the USA, e.g. New York, who has jurisdiction over the validation of wills, the settlement of estates, and the appointment and supervision of guardians
[Latin surrogatus, past part. of surrogare to choose in place of another, substitute, from sur-2 + rogare to ask]