Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sextantārĭus, a, um, adj. [sextans], containing a sextans asses, i. e. worth only the sixth part of the former asses (put in circulation after the second Punic war), Plin. 33, 3, 13, § 44; Fest. p. 347 Müll.