hemistichium
From LSJ
δύο ἀρνήσεις μίαν συγκατάθεσιν ποιοῦσι → two negatives make an affirmative
Latin > English (Lewis & Short)
hēmistĭchĭum: ĭi, n., = ἡμιστίχιον,
I a half-verse, hemistich: Enniano hemistichio usus est, Pseudo Ascon. Cic. Verr. 2, 1, 18.