situated at or extending to great depth; too deep to have been sounded or plumbed;
"the profound depths of the sea"
"the dark unfathomed caves of ocean"
"unplumbed depths of the sea"
"remote and unsounded caverns"
not made to sound;
"the silent `h' at the beginning of `honor'"
"in French certain letters are often unsounded"
- His lungs were unsound.
- The house roof was (structurally) unsound.