‘Trebuša' has its name after the number three (tre). Trebuša is divided in three parts – the upper valley (Gorenja Trebuša), the lower valley (Dolenja Trebuša) and the middle valley. The middle part of the valley does not bear its own name any more. According to the folk tradition there are three different interpretations of the origin of the name ‘Trebuša’. The first one says that the name ‘Trebuša’ originates from the times of charcoal burners. They should have lost three 'buše’, three cows. The second story brings the tale of a man with a huge belly, a ‘trebušnik’. Some say that the name derives from the Italian words 'tre buchi' or 'three holes' (valleys).
According to the oral tradition the eldest house stands in the village Krtovšče, Gorenja Trebuša 112. The Kumar family resided there up until the second half of the 18th century. The year 1792 is carved in stone above the main entrance and means that in this year the house was renovated. Today the house is empty, and it is under the government protection of the national heritage. In 1995 the house got a new thatched roof, which is extremely rare in this area. The other older farmhouses are also the Sedej homestead under Rob (Gorenja Trebuša 111) and a farmhouse on the Prvinski vrh.
Interesting fact: The only object made of stone used to be the church. The first church was build in the middle of the 18th century. The word goes that every villager had to bring a bushel of sand to the spot, where now the church of St. Franciscus Xaverius stands.
Also the homestead at Gorenja Trebuša 16 ‘Pri Mrcini’ has a long tradition. The oldest written records mention the owner of this house already in the frist half of the 18th century. Jakob Ležinar Mrcina, the father, and Gertuda Trušnovec, the mother, had 9 children. The first one was born in 1756. This house is still standing. There are some preserved fresco paintings on the vineyard cottage and on the smithy.
The blacksmiting was besides the glass-making a typical craft in this area. There was a blacksmith at almost every house and at each house they made their own nails. According to the oral tradition the craft of nail-making originates from 200 years ago. These nails were then sold in the village of Čepovan. This craft started to die out in the 1920s.
The area struggled under the consequences of World War II substantially. 10 % of inhabitants died during the war. In 1941 the Liberation Army was constituted in Trebuša. The first partisans arrived to the Trebuša area at the end of 1942. After the capitulation of Italy the liberation movement strengthened. Many inhabitants of Trebuša joined the partisans. Soon after that Germans invaded the valley. Many farmhouses gave shelter to partisans. In some of them provisional hospitals were organised. On 20th of December 1943 the legendary IX Corps was founded in Mrzla Draga. In the small village of Gačnik there were two technical units Jelenk and Špik and in the farmhouse Govec a printing facility called Julij 63. At Rob there existed also a central courier service P-7 for the area of Primorska. The elementary shool with education in Slovenian language was founded in Trebuša in 1944, constantly moving from one house to another in order to be kept secret from Germans.
At the end of World War II Trebuša was economically exhausted and many families were forced to seek work and better living conditions in foreign countries. At present people are moving back to Trebuša, one of the reasons being also the promotion of tourism in this area.