According to the Echoes Songfacts, the lyric, "Numberless names within the force of the ninth wave" is a reference to The Ninth Wave, an 1850 painting by Russian marine artist Ivan Aivazovsky depicting sailors clinging to the mast of a submerged ship after a violent sea storm.
Send out a sound for the wood between the worlds
Gently repeat as the boundaries start to swirl
Keep to the call that is twice now liminal
It's not the same where the trails lead to the outer regions