Language: North Nias
Source: J.A. Feldman e.a.; Nias. Tribal Treasures: Cosmic reflections in stone, wood and gold. 1990.
Introduction
Si euli are a type of knife worn by the people of the north of Nias, a small island to the west of Sumatra. They are relatively rare on the market because most ethnographers and collectors have focused on the more flamboyantly carved styles of the southern part of the island.

An antique si euli from Nias.
Mandarin Mansion inventory, 2023.

Men from North Nias, wearing their si euli.
From De Volken Der Aarde, Deel 1, 1903.
Page 133.
They are found in illustrations published by the Italian explorer Elio Modigliani, who visited the island with only four Javanwse hunters/trackers in 1886 and miraculously made it back alive to write his book. He gives them the name si oli.1 The name si euli which is accepted today appears first in Feldman's study of 1990.2

Swords from North Nias
From Elio Modigliani; Un Viaggio a Nías 1890.
Three main types are shown in the illustration above:
War knives; a, b, and c.
Luxury knives; d, e f, g.
Small everyday knife; h i, j, k.
Notes
1. Elio Modigliani; Un Viaggio a Nías 1890.
2. J.A. Feldman e.a.; Nias. Tribal Treasures: Cosmic reflections in stone, wood and gold. Delft, Volkenkundig Museum Nusantara, 1990. Albert G. van Zonneveld; Traditional Weapons of the Indonesian Archipelago. C. Zwartenkot Art Books, Leiden. Page 123.
In museum collections
A very nice si euli was presented to the Ethnographic Museum in Leiden in 1889. See accession number RV-718-25.