The Charm of Silence is a minor Stealth charm in Ghost of Tsushima. Enemies detect you 15% slower and your Resolve gains rise, from minor to moderate to major as the charm improves. You get it by honoring 24 Inari Shrines.
Follow foxes from fox dens to Inari Shrines and honor them. Once your minor charm slots are all open, further shrines build toward this charm. There are 49 shrines across Izuhara, Toyotama and Kamiagata.
It keeps improving as you honor more Inari Shrines, so finishing the fox dens makes it one of the strongest charms in the game.