aphronitrum
From LSJ
Πρόσεχε τῷ ὑποκειμένῳ ἢ τῇ ἐνεργείᾳ ἢ τῷ δόγματι ἢ τῷ σημαινομένῳ. → Look to the essence of a thing, whether it be a point of doctrine, of practice, or of interpretation.
Latin > English (Lewis & Short)
ā̆phrŏnī̆trum: i, n., = ἀφρόνιτρον,
I the efflorescence of saltpetre, Plin. 31, 10, 46, § 3; Mart. 14, 58.
Latin > French (Gaffiot 2016)
aphrŏnitrum, ī, n. (ἀφρόνιτρον), écume ou fleur de nitre : Plin. 31, 113.