Lewis & Short

in-sŏnus a, um, adj., without sound, noiseless, silent (post-class.).

  1. I. Lit.: passus, Amm. 27, 12; cf. gressus, id. 29, 5: vestigium, App. M. 3, p. 138, 22.
  2. II. Transf.: litterae, i. e. mutae, App. de Mundo, p. 66, 29.