The Collaborative International Dictionary of English v.0.48:

Headway \Head"way`\ (-w[^u]rk`), n.
   1. The progress made by a ship in motion; hence, progress or
      success of any kind.
      [1913 Webster]

   2. (Arch.) Clear space under an arch, girder, and the like,
      sufficient to allow of easy passing underneath; clearance;
      headroom.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "headway":
   Great Leap Forward, advance, advancement, advancing, amelioration,
   amendment, anabasis, ascent, bettering, betterment, boost, career,
   course, driftway, enhancement, enrichment, eugenics, euthenics,
   forward motion, forwardal, forwarding, furtherance, furthering,
   gain ground, get ahead, get going, go, go ahead, go-ahead,
   improvement, leeway, lift, make headway, march, melioration, mend,
   mending, move forward, ongoing, onward course, passage, pickup,
   preferment, proceed, proficiency, progress, progression,
   progressiveness, promotion, recovery, restoration, revival, rise,
   rolling, rolling on, steerageway, sternway, travel, upbeat, uplift,
   upping, upswing, uptrend, upward mobility, way