The Collaborative International Dictionary of English v.0.48:

Megalophonous \Meg`a*loph"o*nous\
   (m[e^]g`[.a]*l[o^]f"[-o]*n[u^]s), a. [Megalo- + Gr. fwnh`
   voice.]
   Having a loud voice.
   [1913 Webster] Megapolis