κατασιωπητέον
From LSJ
Ὁ μὲν βίος βραχύς, ἡ δὲ τέχνη μακρή, ὁ δὲ καιρὸς ὀξύς, ἡ δὲ πεῖρα σφαλερή, ἡ δὲ κρίσις χαλεπή → Life is short, art long, opportunity fleeting, experience misleading and judgment difficult
English (LSJ)
one must keep silence, Isoc.12.96.
Greek (Liddell-Scott)
κατασιωπητέον: ῥημ. ἐπίθ., πρέπει νὰ κατασιωπᾷ τις περί τινος, περί τινος κατασιωπητέον Ἰσοκρ. 252D.
French (Bailly abrégé)
adj. verb. de κατασιωπάω.