The surname is a place-name derived from Ormstown.   Orm, son of Hugh of Abernethy, gave his name to Ormiston, in East Lothian, and Orm, son of Acolf of Ashkirk, to Ormiston in Selkirkshire, but no family derives its name from these places.

The Scottish surname is derived from Ormiston in Teviotdale, Eckford parish, in Roxburgh-shire at the junction of the Kale with the river Teviot. In the early part of the twelfth century, it was owned by Orm, son of Eilaf of the house of Gospatric. When he founded the estate of Orms-town, Ormiston, Ormston, or other variants of the spelling, became surnames. John, the son of Orm, was the second sheriff of Roxburghshire.

This Orm of Ormston, was named after Orm, son of Kebel, husband of Gunilda, sister of Gospatric II. He witnessed, in 1136, a charter by which King David I granted Melrose to the monks of Melrose. And with Gospatric IV, his cousin, in 1159, he witnessed a charter of King Malcolm IV, his third cousin’s son. He, his son John, and his cousin Gospatric, witnessed another charter of Malcolm, granting to the church of Glasgow the church of old Roxburgh.

John's son was William, who assumed the surname of De Laundeles, and to a charter of John de Laundeles, son of this William, in the reign of Alexander II (1214-1249), we find Alanus de Hormiston was a witness.

About the same time, in 1244, William de Ormiston was one of the knights "who have sworn with Earl Patrick."

In 1296, with other Ormistons, John de Ormiston signed the “Ragman Roll” or instrument of submission to Edward I of England. The seal of this John, attached to the Roll, shows the pelican, with afterwards became the armorial bearings of the family.

These are the earliest instances of the use of Ormiston as a surname.

It is impossible to say from which branch off the main, or sub-branch, any particular family of Ormistons or Ormstons sprang without their possession of a clear line of descent, but it is undoubted that any of the name whose ancestors came from Scotland are descended from the Teviotdale Ormistons, and they may have branched off any time from the thirteenth to the seventeenth century, but more likely between the fifteenth and seventeenth. In early times surnames were unknown, and people were given names to distinguish them one from another, and frequently a person’s trade gave him a name; for instance, an armourer was called "Smith," and to distinguish one Smith from another Christian names came into being.

Orm was simply a personal name given to the son of Eilaf, after Orm, son of Kebel, husband of Gunhilda, Eilaf’s aunt. Any name beginning with Orm was originally derived from the word Orm, which means a worm or serpent. The Icelandic Orm-r means a snake or worm, and Orm was a personal name not uncommon in Saxon and Norman times, and is doubtless of Scandinavian origin, as it was a favourite Scandinavian name. In old Norse the generic name for serpents is Orm, and this name was applied to Viking ships having a dragon’s head at the bows and a curled tail at the stern, and the shields arranged along the sides represented the scales. Great Orm’s Head means the great serpent’s head. The word worm is derived from Orm.