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

• time capsule
• time clock
• time constant
• time deposit
• time deposit account
• time draft
• time exposure
• time frame
• time immemorial
• time interval
• time lag
• time limit
• time loan
• time machine
• time note
• time of arrival
• time of day
• time of departure
• time of life
• time of origin
• time of year
• time off
• time out of mind
• time period
• time plan