Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
auctārĭum, ii, n. [augeo], an addition or augmentation of a definite measure: auctarium dicebant antiqui, quod super mensuram vel pondus justum adiciebatur, Paul. ex Fest. p. 14 Müll.: Eu. Tanti quanti poscit, vin tanti illum emi? Ch. Immo auctarium Adicito, Plaut. Merc. 2, 4, 23.