From The Collaborative International Dictionary of English v.0.48 :
Quag \Quag\, n.
A quagmire. [R.] "Crooked or straight, through quags or
thorny dells." --Cowper.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
quag
n 1: a soft wet area of low-lying land that sinks underfoot
[syn: mire, quagmire, quag, morass, slack]