Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
* illustrātĭo (inl-), ōnis, f. [illustro], in rhetoric, vivid representation: insequetur ἐνάργεια, quae a Cicerone illustratio et evidentia nominatur, quae non tam dicere videtur quam ostendere, Quint. 6, 2, 32.