Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
căchinnātĭo, ōnis, f. [cachinno], a violent laughing, immoderate laughter: sine ullā suspitione nimiae suspitionis, Auct. Her. 3, 14, 25: ut si ridere concessum sit, vituperetur tamen cachinnatio, Cic. Tusc. 4, 31, 66.