Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ădoptātor, ōris, m. [id.; access. form of adoptio, by which it was supplanted after the class. per.], one that adopts another, an adopter, Gell. 5, 19; Dig. 37, 9, 1, § 12 med.