Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
auctĭōnārĭus, a, um, adj. [auctio], of or pertaining to an auction, auction-: atria, wherein auctions were held, Cic. Agr. 1, 3; Inscr. Orell. 3883 (v. atrium): tabulae, catalogues of goods to be sold by auction, Cic. Cat. 2, 8, 18.