中英語のswam「沼地」、中英語のsompe「沼地」からの混成語で、どちらも最終的には原ゲルマン語の*sumpaz「沼地」、「泥沼」、語源はsumpと同じである。
[B]y swamps then in general is to be understood any low grounds subject to inundations, distinguished from marshes, in having a large growth of timber, and much underwood, canes, reeds, wythes, vines, briers, and such like, so matted together, that they are in a great measure impenetrable to man or beast .... [Bernard Romans, "A Concise History of East and West Florida," 1775]More popular in U.S. (swamp (n.) by itself is first attested 1624 in Capt. John Smith's description of Virginia). Swamp-oak is from 1680s, American English. Swamp Yankee "rural, rustic New Englander" is attested from 1941. Thornton's "American Glossary" (1912) has swamp-angel "dweller in a swamp," swamp-law "might makes right."