The Collaborative International Dictionary of English v.0.48:

Quagmire \Quag"mire`\, n. [Quake + mire.]
   Soft, wet, miry land, which shakes or yields under the feet.
   "A spot surrounded by quagmires, which rendered it difficult
   of access." --Palfrey.
   [1913 Webster]

   Syn: Morass; marsh; bog; swamp; fen; slough.
        [1913 Webster] Quahog

WordNet (r) 3.0 (2006):

quagmire
    n 1: a soft wet area of low-lying land that sinks underfoot
         [syn: mire, quagmire, quag, morass, slack]