Is it farther or further?
c.1600, from French tacite, from Latin tacitus "that is passed over in silence, done without words, assumed, silent," prop. past participle of tacere "to be silent," from PIE root *tak- "to be silent" (cf. Gothic þahan, Old Norse þegja "to be silent," Old Norse þagna "to grow dumb," Old Saxon thagian, Old High German dagen "to be silent"). The musical instruction tacet is the 3rd person present singular of the Latin verb.