n.
   - the distance from the top or surface to the bottom of something or to a specified point within it. 
▸the distance from the front to the back of something.
 ▸the apparent existence of three dimensions in a two-dimensional representation.
 - the quality of being intense or extreme. 
▸complexity and profundity of thought.
 ▸comprehensiveness of study or detail:
 third-year courses go into more depth.
 - 
(the depths)
 the deepest or lowest part of something.
 
 
  Phrase
  
    - hidden depths
 previously unnoticed qualities.  - in depth
 in great detail; comprehensively and thoroughly.  - out of one's depth
  - in water too deep to stand in.
 - in a situation beyond one's capabilities.
 
 
   
  Etymology
  ME: from deep + -th2, on the pattern of pairs such as long, length.