Lewis & Short

Pĕtŏsīris, ĭdis, m., = Πετόσιρις, a celebrated Egyptian mathematician and astrologer, Plin. 2, 23, 21, § 88; 7, 49, 50, § 160; Firm. Math. 4, praef.
Hence, transf., a great mathematician, astrologer, in gen., Juv. 6, 580.