What is a real word that means "disenthused"?

Solution 1:

You may use dispirit:

  • Cause (someone) to lose enthusiasm or hope: (ODO)

    • the army was dispirited by the uncomfortable winter conditions

or disappoint:

  • fail to satisfy the hope, desire, or expectation of. (AHD)
  • I was dispirited / disappointed by what I saw.

Solution 2:

Unenthused is a real word, at least in British English.

http://www.oxforddictionaries.com/definition/english/unenthused