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"-Thomas Gray; "unplumbed depths of the sea"; "remote and unsounded caverns"

To present participles which come from intransitive verbs, or are themselves employed as adjectives, to mark the absence of the activity, disposition, or condition implied by the participle;

not made to sound; "the silent `h' at the beginning of `honor'"; "in French certain letters are often unsounded"