The Collaborative International Dictionary of English v.0.48:

Weltschmertz \Welt"schmertz`\ (v[e^]lt"shm[e^]rts`), n. [G., fr.
   welt world + schmertz pain. See World; Smart, v. i.]
   Sorrow or sadness over the present or future evils or woes of
   the world in general; sentimental pessimism.
   [Webster 1913 Suppl.]