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

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]

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