Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
tergiversātor, ōris, m. [tergiversor], one who delays, declines, o hangs back, a boggler, laggard (post-class.), Gell. 11, 7, 9; Arn. 7, 247; cf. Isid. 10, 271.