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

• Second Epistle to Timothy
• second estate
• first-class honors degree
• first-class honours degree
• first-class mail
• first-come-first-serve
• first-degree burn
• first-generation
• first-nighter
• first-order correlation
• first-place finish
• first-rate
• first-rater
• first-string
• first-time buyer
• first-year
• firstborn
• firsthand
• firstling
• firstly
• firth
• Firth of Clyde
• Firth of Forth
• FISA
• fisc