“De-” as in “down” and the root is related to “voracious”.  Thus, to “gulp down”.

• 01.109 certainly not after devouring so many of the dwarves
• 05.055 This thing all things devours:
• 06.063 and devouring people waked suddenly from their sleep.

“devour, v.” OED Online. Oxford University Press, June 2015. Web. 27 July 2015.