Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
†† rasta, ae, f. [Germ.; O. H. Germ. rasta or rast, rest; Goth. rasta, a mile; cf. the Slav. werst], a German measure of a mile (late Lat.), Hier. in Joel, 3, 18.