喪家之狗

Etymology
From the :

喪家之狗 was later reanalysed as "a dog that has lost its home", which would often go hungry and wander the streets in search for food, due to neglect by its master. Later, this became a metaphor for a desperate person who has nobody to turn to.

Idiom

 * 1)  a stray dog
 * 2)  a desperate person who has nobody to turn to