profound, unfathomed, unplumbed, unsounded -- (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")
silent, unsounded -- (not made to sound; "the silent `h' at the beginning of `honor'"; "in French certain letters are often unsounded")
(TTS Sound)
