Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Ăgăthyrsi, ōrum, m., = Ἀγάθυρσοι, a Scythian people (in what is now Transylvania, and the Bannat of Temeswar) who commonly painted their faces and limbs; hence Vergil: picti Agathyrsi, A. 4, 146; cf. Plin. 4, 12, 26; and Mel. 2, 1.