One description of the river's naming was recorded in 1945 by George R. Stewart, but is now considered to be a folk tale:[10]
...remembering how they had been served at the Whore-Kill, they went some ten or twelve miles higher, where they landed again and traded with the Indians, trusting the Indians to come onto their stores ashore, and likewise aboard their sloop drinking and debauching with the Indians until they were at last barbarously murdered, and so that place was christened with their blood and to this day is called the Murderer-Kill, that is, Murderers Creek.[11]
— George R. Stewart, Names on the Land: A Historical Account of Place-Naming in the United States
Dick Carter, Chair of the Delaware Heritage Commission, states that the name of Murderkill River is taken from the original Dutch for Mother River. Mother is moeder in Middle Dutch, and river is Kille. Later, under British rule, the word "River" was added to the waterway's name, effectively making it "mother river river."[10] The term "kill" is used in areas of Dutch influence in the Netherlands' former North American colony of New Netherland, primarily the Hudson and Delaware Valleys to describe a creek, river, tidal inlet, strait, or arm of the, sea such as Bronx Kill in New York and Schuylkill River in Pennsylvania.
Delaware's creeks and rivers are slow-moving and there is deep mud associated with marshy rivers. Dutch "modder" = mud, a false cognate to "mother." Modder Kill = Muddy Creek or Muddy River. The word is still used in Dutch, such as this Dutch video of a tractor stuck in mud ("vast in de modder").[12]
Quakers had a Meeting House nearby; in Delaware they often named their meetings after a waterway (see e.g., Appoquinimink Friends Meetinghouse, further north; Duck Creek Meeting; or very early George's Creek Meeting). They disliked the name Murderkill and went with "Motherkiln" and "Motherkill." It's possible they originated the alternative names or were choosing among local variants. [13]
Also, in New York there is Muddy Kill, with a clear connection to the older Dutch name.
