1. Situated at or extending to great depth; too deep to have been sounded or plumbed
   "remote and unsounded caverns"
   - profound, unfathomed, unplumbed 
2. Not made to sound
   "in French certain letters are often unsounded"
   - silent

See also: deep, inaudible, unhearable

• buck sergeant
• buck up
• buck's fizz
• buck-and-wing
• buck-passing
• buck-toothed
• buckaroo
• brainchild
• brainiac
• brainish
• brainless
• brainpan
• brainpower
• brains trust
• brainsick
• brainstem
• brainstorm
• brainstorming
• brainwash
• brainwashed
• brainwashing
• brainwave
• brainworker
• brainy
• braise