Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
arrūgĭa, ae, f. [akin to runco, runcina, ὀρύσσω, ὀρύξω, to dig; cf. Corssen, Ausspr. I. p. 543; v. corrugus], a shaft and pit in a gold-mine, Plin. 33, 4, 21, § 70.