Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rădĭātĭo, ōnis, f. [radio], a glittering, shining, a beamy lustre, radiation (postAug.): marmoris, Plin. 36, 5, 4, § 32: stellarum, Jul. Firm. Math. 1, 4.
Plur., Arn. 6, 208.