The national flag of Great Britain and Ireland, which combines the banner of St. Patrick with the crosses of St. George and St. Andrew. The word “jack” is most probably derived from the surcoat, charged with a red cross, anciently used by the English soldiery. This appears to have beeu called a “Jacque,” whence the word “Jacket,” anciently written “Jacqult.” Some, however, without a shadow of evl-dence, derive the word from "Jacques” the first alteration having been made in the reign of King James I. wharton
Source: Black's Law Dictionary 2nd Ed (1910)
