I. ˈsau̇ndlə̇s, in rapid speech -nl- adjective
Etymology: obsolete English sound act of sounding + English -less — more at sound (probing instrument)
: incapable of being sounded or plumbed : unfathomable
soundless seas
the soundless deep
II. adjective
Etymology: sound (III) + -less
: making no sound : quiet , silent
tread sure and soundless — Lew Wallace
his mouth moving in a brief, soundless prayer — Josephine Johnson