with hushed footsteps; stealthily; quietly
Describes moving quietly so as not to be heard; often used in narrative or descriptive contexts.
See also: 殺す (ころす)
He walked down the hallway with hushed footsteps.
The burglar entered the house stealthily.
A set phrase combining 足音 (footsteps) with 殺して (the te-form of 殺す, here meaning 'to suppress' or 'to kill' the sound). The expression literally means 'killing the sound of footsteps'.