Source : Webster's Revised Unabridged Dictionary (1913)

Quag \Quag\, n.
   A quagmire. [R.] ``Crooked or straight, through quags or
   thorny dells.'' --Cowper.

Source : WordNet®

quag
     n : a soft wet area of low-lying land that sinks underfoot [syn:
          {mire}, {quagmire}, {morass}]