Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
vī̆brātĭo, ōnis, f. [vibro], a brandishing, vibration: hastae, Fest. s. v. gradivus, p. 97: continuata tonitruum, Calp. ap. Vop. Carin. 8.