(as) silent as the grave simile
Very quite
That house always gives me the creeps because it's as silent as the grave.
As the darkness falls upon the village, the streets become silent as the grave.
It is so quiet that you would be able to hear even the tiniest sounds.
Extremely quiet.
Used when one suddenly becomes quiet because one is nervous, upset, or does not want to mention a particular topic.
Do something silently, secretly.
1. To keep silent.
2. To prevent someone from divulging information.
The origin of this phrase is not clear, probably based on the figurative usage of the word "grave".