HARPOKRATES (Harpocrates) was the god of silence.
Harpokrates was the Greek interpretation of the Egyptian god Harpa-Khruti (Horus the Child) who was usually depicted as a small boy with a finger held to his lips--an Egyptian gesture symbolising childhood which the Greeks mistook for a hush for silence.
"[The Egyptian goddess] Isis first invented sails, for while seeking her son Harpocrates [Horus], she sailed on a ship."
"She saw before her bed, or seemed to see as in a dream, great [Egyptian goddess] Isis with her train of holy deities. Upon her brow there stood the crescent moon-horns, garlanded with glittering heads of golden grain, and grace of royal dignity; and at her side . . . [Harpocrates] the god who holds his finger to his lips for silence's sake."
"Upon her [the Egyptian goddess Isis'] brow stood the crescent moon-horns, garlanded with glittering heads of golden grain, and grace of royal dignity; and at her side the baying dog Anubis, dappled Apis, sacred Bubastis and the god [Harpocrates] who holds his finger to his lips for silence sake."
Other references not currently quoted here: Augustine City of God 18.5, Varro On the Latin Language 5.57, Catullus 102, Erasmus Adages 4.1.52.