しいんと (する)
しいんと (する) · shiinto (suru) · JLPT N2 · noun
silent
🤫 shiin = 'shh' sound: silence falls, then it's shiinto (quiet as a grave)
The 'shiin' sound mimics a hush, like saying 'shh' to a room. する turns it into a verb: the room goes shiinto, deathly quiet.