Source : Webster's Revised Unabridged Dictionary (1913)

Columnar \Co*lum"*nar\, a. [L. columnaris, fr. columna.]
   Formed in columns; having the form of a column or columns;
   like the shaft of a column.

   {Columnar epithelium} (Anat.), epithelium in which the cells
      are prismatic in form, and set upright on the surface they
      cover.

   {Columnar structure} (Geol.), a structure consisting of more
      or less regular columns, usually six-sided, but sometimes
      with eight or more sides. The columns are often fractured
      transversely, with a cup joint, showing a concave surface
      above. This structure is characteristic of certain igneous
      rocks, as basalt, and is due to contraction in cooling.

Source : WordNet®

columnar
     adj 1: having the form of a column; "trees with columned trunks";
            "columnar forms"; "a columnlike tree trunk" [syn: {columniform},
             {columnlike}]
     2: characterized by columns; "columnar construction"