headroom

from WordNet (r) 3.0 (2006)

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

from The Collaborative International Dictionary of English v.0.48

Headroom \Head"room`\ (-r[=oo]m`), n. (Arch.)
   See {Headway}, 2. [Mostly Brit.]
   [1913 Webster +PJC]