The word means, to open, or make open. It was to be written in open and plain letters, and on tables or tablets. These were either of wood or stone, made smooth. The Septuagint render the word πυξιον, a smooth plank of boxwood, and give the whole sentence thus: “Write the vision and openly (or plainly—σαφῶς,) on boxwood.”
See Deuteronomy 27:8. So Junius takes the word as an adverb, perspicue, perspicuously.—Ed.