The Collaborative International Dictionary of English v.0.48:

Synclinal \Syn*cli"nal\, a. [Gr. ? to incline together; sy`n
   with + ? to incline.]
   1. Inclined downward from opposite directions, so as to meet
      in a common point or line.
      [1913 Webster]

   2. (Geol.) Formed by strata dipping toward a common line or
      plane; as, a synclinal trough or valley; a synclinal fold;
      -- opposed to anticlinal.
      [1913 Webster]

   Note: A downward flexure in the case of folded rocks makes a
         synclinal axis, and the alternating upward flexure an
         anticlinal axis.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Synclinal \Syn*cli"nal\, n. (Geol.)
   A synclinal fold.
   [1913 Webster]

WordNet (r) 3.0 (2006):

synclinal
    adj 1: sloping downward toward each other to create a trough
           [ant: anticlinal]