Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
obrŏgātĭo, ōnis, f. [obrogo], a motion partly to repeal or alter one law by another, an obrogation: cum duae leges inter se differunt, videndum est, num qua obrogatio aut derogatio sit, Auct. Her. 2, 10, 15; cf. obrogo.