Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
obvŏlūtĭo, ōnis, f. [obvolvo], a wrapping round, enveloping; an envelope (postclass.): aetherea obvolutio, Macr. Somn. Scip. 1, 11, § 12; Cael. Aur. Acut. 2, 11, 79.