Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
circĭnātĭo, ōnis, f. [circino] (lit. the describing of a circle; hence, concrete), the circumference of a circle, a circle (a word of Vitr.): linea circinationis, Vitr. 1, 6, 6: circuli, id. 9, 7, 2; 3, 3; 10, 10 al.
Of the circular path of the planets, Vitr. 9, 4, pp. 264, 266 Bip.