silently
adverb /ˈsaɪləntli/
  /ˈsaɪləntli/
Idioms - without speaking- They marched silently through the streets.
 
- without making any or much sound synonym quietly- She crept silently out of the room.
- The car rolled silently downhill.
 
- without using words or sounds to express something- She prayed silently.
- He silently agreed with much of what she had said.
 
Idioms 
sit/stand silently by 
- to do or say nothing to help somebody or deal with a difficult situation- We can’t sit silently by and let them arrest him!