Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
nōnāgēni, ae, a (gen. pl. nonagenūm, Front. Aquaed. 61), adj. distr. [nonaginta], ninety each: porticus ascenduntur nonagenis gradibus omnes, Plin. 36, 13, 19, § 88.