QUAGMIRE, a bog or marsh, a piece of ground so saturated with water that it cannot support any weight. The word is composed of " quag " or " quake " (O.E. cwacian; cf. " quaver," " quiver ") and " mire, "mud (Icel. myri, Swed. myr).
Skeat suggests that quag may be connected with the root seen in " quick," and quotes (Etym. Diet. 1898) Piers Plowman, c. xxi. 64, of an earthquake, the earth " quook as it quyke were," i.e. shook as if it were alive.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)