Source : Webster's Revised Unabridged Dictionary (1913)

Headway \Head"way`\, n.
   1. The progress made by a ship in motion; hence, progress or
      success of any kind.

   2. (Arch.) Clear space under an arch, girder, and the like,
      sufficient to allow of easy passing underneath.

Source : WordNet®

headway
     n 1: vertical space available to allow easy passage under
          something [syn: {headroom}, {clearance}]
     2: forward movement; "the ship made little headway against the
        gale" [syn: {head}]