To speak clearly (eloquently)
He spoke in clear, precise, or beautiful language (צַח literally means pure or clean).
("And the heart of the discerning will understand knowledge; and the tongue of the stammerers will hasten to speak clearly" - Isaiah 30:4)
Translation
Expression (Hebrew)
דִּבֵּר צַחוּת
Definition (Hebrew)
דִּבֵּר בְּלָשׁוֹן בְּרוּרָה, מְדֻיֶּקֶת אוֹ יָפֶה (צַח מִשְׁמָעוֹ זַךְ אוֹ טָהוֹר).
("וּלְבַב נִמְהָרִים יָבִין לָדָעַת וּלְשׁוֹן עִלְּגִים תְּמַהֵר לְדַבֵּר צָחוֹת"- יְשַׁעְיָהוּ לֵב ד)