Source : Webster's Revised Unabridged Dictionary (1913)

Longitudinal \Lon`gi*tu"di*nal\, n.
   A railway sleeper lying parallel with the rail.

Longitudinal \Lon`gi*tu"di*nal\, a. [Cf. F. longitudinal.]
   1. Of or pertaining to longitude or length; as, longitudinal
      distance.

   2. Extending in length; in the direction of the length;
      running lengthwise, as distinguished from transverse; as,
      the longitudinal diameter of a body. --Cheyne.

Source : WordNet®

longitudinal
     adj 1: of or relating to lines of longitude; "longitudinal
            reckoning by the navigator"
     2: running lengthwise; "a thin longitudinal strip";
        "longitudinal measurements of the hull"
     3: over an extended time; "a longitudinal study of twins"