Posidonius
From LSJ
περὶ οὐδὲν γὰρ οὕτως ὑπάρχει τῶν ἀνθρωπίνων ἔργων βεβαιότης ὡς περὶ τὰς ἐνεργείας τὰς κατ' ἀρετήν → since none of man's functions possess the quality of permanence so fully as the activities in conformity with virtue
Latin > English (Lewis & Short)
Pŏsīdōnĭus: ii, m., = Ποσειδώνιος,
I a celebrated Stoic at Rhodes, a disciple of Panœtius and instructor of Cicero, Cic. Att. 2, 1, 2; id. Off. 3, 2, 8; id. N. D. 1, 3, 6; id. Div. 1, 3, 6 al.