The Collaborative International Dictionary of English v.0.48:

Helicon \Hel"i*con\ (h[e^]l"[i^]*k[o^]n), prop. n. [L., fr. Gr.
   "Elikw`n.]
   A mountain in B[oe]otia, in Greece, supposed by the Greeks to
   be the residence of Apollo and the Muses.
   [1913 Webster]

         From Helicon's harmonious springs
         A thousand rills their mazy progress take. --Gray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

helicon
    n 1: a tuba that coils over the shoulder of the musician [syn:
         helicon, bombardon]