The slang term minge in the sense of quim dates from the beginning of the 20th century. However, neither the OED nor Etymonline has any idea where it came from. Here are two of its citations: 1936 ...
Both the OED and Etymonline offer no clue as to origin of the slang term quim, meaning minge. The OED’s earliest citations are from the 18th, which isn’t quite as old as Adam, but has certainly been ...