Wordnet 3.0
ADJECTIVE (1)
1. 
 of or taking place in the deeper parts of the sea; 
- Example: "deep-sea fishing"- Example: "deep-sea exploration"
The Collaborative International Dictionary of English v.0.48:
Deep-sea \Deep"-sea`\, a.
   Of or pertaining to the deeper parts of the sea; as, a
   deep-sea line (i. e., a line to take soundings at a great
   depth); deep-sea lead; deep-sea soundings, explorations, etc.
   [1913 Webster]
   2. at some distance from the shore; as, deep-sea fishing.
   Syn: offshore.
        [WordNet 1.5 +PJC]
   3. taking place in the deeper parts of the sea; as, deep-sea
      exploration.
      [WordNet 1.5]
WordNet (r) 3.0 (2006):
deep-sea
    adj 1: of or taking place in the deeper parts of the sea; "deep-
           sea fishing"; "deep-sea exploration"