The Oxford English Dictionary assures me that the oldest known use of the word standard was as the name of this battle; The Battle of Standard.

In Eng. the word appears first with reference to the `Battle of the Standard’ in 1138. A contemporary writer, Richard of Hexham, relating the story of the battle, describes the `standard’ there used as a mast of a ship, with flags at the top, mounted in the middle of a machine which was brought into the field. He quotes a Latin couplet written on the occasion, which says that the standard was so called from `stand’, because `it was there that valour took its stand to conquer or die’.

The editors of the OED also spend far too much time fighting the losing battle that a standard is a triangular flag while a rectangular flag is a banner; except of course the Queen’s standard which is a rectangle.