Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
grăvātĭo, ōnis, f. [gravo], heaviness, oppression (post-class.): post cibum, Cael. Aur. Acut. 2, 32, 171; id. Tard. 5, 10, 96; 4, 3, 33.