Trews (Gaelic Truis or older Truibhs) are men's clothing for the legs and lower abdomen, a traditional form of Scottish clothing. Trews could be trimmed with leather, probably buckskin, especially on the inner leg to prevent wear from riding on horseback.
Trews may be the origin of the word trousers in English.
Tartan trews shared the fate of other items of Highland dress, including proscription under the Dress Act of 1746 that banned Highlanders from wearing the truis ("Trowse"), and resurrection during the Romantic Revival.
Illustrations in the Book of Kells and on the Cross of Muiredach show soldiers wearing short truis-like garments which reached to just above or just below the knee. Those illustrated in the Book of Kells are of a single colour, tight-fitting and end below the knee while those shown on the cross panel are loose-fitting, striped and gathered just above the knee. Also illustrated in the Book of Kells are long tight-fitting truis which are secured by loops under the foot.
The word is triubhas in Scottish Gaelic. Truis or trews are anglicised spellings.
- Edward Dwelly, Faclair Gàidhlig gu Beurla: Illustrated Gaelic to English Dictionary
- Colin Mark, The Gaelic-English Dictionary
Traditional trews were form-fitting garments, similar to the footed hose of the Renaissance, from which they probably evolved. They could be cut as Knee-breeches or full length.
These trews were cut on the cross-grain (US bias), which allowed the fabric to stretch sufficiently to mould to the body, and placed the tartan "sett" on the diagonal.
Traditional trews are actually long hose. These hose came all the way up to the waist and were attached to a linen cloth (NB: These were not trousers). They were fastened at the lower leg, below the knee, by a garter (the precursor to the flashes of the Highland Dress) as can be seen in the painting by David Morier of the Battle of Culloden. It is said in Scottish Tradition Lore that these truibhas were actually the common garment of the 16th to 18th Centuries in the Highlands. It is also a fascinating note that when travelling, in order to avoid getting the trews wet when crossing streams, the Highlander would wear shorter hose, ones that would only reach up to the knee, and wrap his "bed-garments" around his waist, a form of the Great Kilt.
Modern trews and military trews
Modern trews are more like trousers with the fabric cut on the straight grain but without a side seam, and are often high-waisted, to be worn with a short jacket, as a warmer alternative to the kilt.
Colonel Sir John Sinclair of the Caithness, proved to his own satisfaction that "the truis" was an older dress than kilts. 
Until the establishment of the Royal Regiment of Scotland in 2006, military trews were usually worn by members of the lowland Scottish regiments as part of their No 1, mess and full dress uniforms. Members of highland Scottish regiments were usually authorized to wear kilts with these orders of dress. However, all Highland regiments, in more recent times, wore trews with less formal orders of barracks and training dress. They were also part of the uniform of the composite regiment known as The Highlanders (Seaforth, Gordons and Camerons) formed in 1994. The new Royal Regiment of Scotland comprises all the former Scottish infantry line infantry regiments and continues to wear trews in certain limited orders of dress.
Historically trews were part of the Highland cultural tradition, not Lowland. As such, when Lowland regiments became the first of the Scottish regiments to be formed in the mid-1660s to late 1680s, the Lowland soldiers wore standard British military uniform and had no desire to wear tartan items and march to the bagpipes, which they considered to be part of a foreign and savage culture. From these early beginnings up to 1881, the famous Lowland regiments (1st, 21st, 25th, 26th, 70th, 90th, 94th and 99th) wore standard English uniform.
Meanwhile, from 1739 onward, the Highland regiments which were raised insisted on the familiarity of their native dress and Great Highland war-pipes, albeit in a modified form to suit a British military identity, as part of their cultural identity. They wore the complex belted plaid and latterly, to encourage recruits unfamiliar with such garb, they adopted the simpler kilt. However, trews were increasingly worn as off-duty dress and even campaign dress from the late 18th Century. Highland regiments stationed in hot or unhealthy surroundings often took to wearing simple white cotton trousers or tartan trews. For example, the 91st Highland Regt of Foot wore trews during the Walcheren campaign of 1809 and more famously, the 93rd Highland Regiment of Foot wore trews and round unfeathered Highland bonnets during the war of 1812-1815 against the USA, when taking part in the British campaign to capture New Orleans in January 1815 and during the disastrous Battle of Chalmette Plain itself (lithographs of the battle wrongly depict them wearing kilts).
In 1822, following King George IV's successful first visit to Scotland including a separate coronation, he ordered the resumption of Highland dress and traditions for one de-kilted regiment. The regiment chosen was the most senior of the de-kilted regiments, the 72nd. They adopted the Highland feather bonnet, the Highland version of the red coatee, but in lieu of kilts, they were ordered to wear trews for all duties. The tartan chosen was a new form of red or Royal Stewart called Prince Charles Edward Stuart, reflecting the new romantic fashion for all things Jacobite.
Due to the military use of trews by the Lowland regiments, the perception of trews as Lowland dress spilled over into civilian wear, so that for many years, trews began to be viewed as Lowland dress, rather than the Highland kilt. However, in recent years, a resurgence in Highland history and traditions has seen trews re-enter the Highland wardrobe, whilst interested Lowlanders have now encompassed these traditions within a wider Scottish template.
Today, the sideways kicking step of Scottish highland dancers performing the Seann Truibhas dance is said to symbolise the kicking off of the trews or trousers in favour of the kilt, through the trews can still be worn today as a warmer alternative to the kilt in colder months, as shown in the gallery picture below.
Considering that tartan trews were part of the Highland wardrobe for chieftains and gentlemen whilst on horseback (the large Highland ponies) from the early 1600s onward, it is more likely that the 'Truibhas' in the dance represent English-style plain trousers (breeches), adopted under duress by Highlanders following the ban on their native Highland kilted dress effective from 1st August 1746 to its repeal on 1st July 1782.
Plus-fours and golf attire
Tartan plus-fours are traditional golfing attire that are based on the traditional trews. These pants extend 4 inches below the knee and are often worn with argyle knee-socks. Plus-fours were first introduced to the USA by the Prince of Wales during a 1924 visit. The full-length plaid pants popular with many golfers are also based on trews, but are cut fuller for more freedom of movement and warmer climates.
- James MacDonald Reid, Notes on Scottish Lore, 2009
- James MacDonald Reid, Notes on Scottish Lore, 2009