Godan verb with 'ru' ending, Intransitive verb
to become quiet; to quiet down; to quieten down
esp. 静まる
シンと静まった部室。響くのは、クロッキー帳に擦れる鉛筆の音だけ。The club room returned to quiet. All that could be heard was the sound of pencil on sketchpad. to calm down; to die down; to subside; to abate; to be suppressed
esp. 鎮まる
Also written 鎮まる【しずまる】