WordWeb Online

1. The intellectual ability to penetrate deeply into ideas
   - astuteness, profundity, profoundness, depth
    
2. The quality of being physically deep
   "the deepness of the mine was almost a mile"
   - profundity, profoundness
    
3. The extent downward or backward or inward
   "the deepness of the water"
   - depth
    
4. A low pitch that is loud and voluminous

Derived forms: deepnesses

See also: deep, shallow

Type of: extent, low frequency, low pitch, sapience, wisdom

Antonym: shallowness