1604, from Fr. tacite, from L. tacitus "that is passed over in silence, done without words, assumed, silent," prop. pp. of tacere "to be silent," from PIE base *tak- "to be silent" (cf. Goth. þahan, O.N. þegja "to be silent," O.N. þagna "to grow dumb," O.S. thagian, O.H.G. dagen "to
be silent"). The musical instruction tacet is the 3rd person present sing. of the L. verb.