Source : Webster's Revised Unabridged Dictionary (1913)

Headroom \Head"room`\, n. (Arch.)
   See {Headway}, 2.

Source : WordNet®

headroom
     n 1: vertical space available to allow easy passage under
          something [syn: {headway}, {clearance}]
     2: the capacity of a system to reproduce loud sounds without
        distortion [syn: {dynamic headroom}]