Syunik (Old Armenian: Սիւնիք, romanized: Siwnik') was a region of historical Armenia and the ninth province (nahang) of the Kingdom of Armenia from 189 BC until 428 AD. From the 7th to 9th centuries, it fell under Arab control. In 821, it formed two Armenian principalities: Kingdom of Syunik and principality of Khachen, which around the year 1000 was proclaimed the Kingdom of Artsakh, becoming one of the last medieval eastern Armenian kingdoms and principalities to maintain its autonomy following the Turkic invasions of the 11th to 14th centuries.

The name Syunik is ancient and appears in the earliest Armenian written sources. Sisakan, a later name for the province of Iranian origin, first appears in the 6th-century Syriac chronicle of Pseudo-Zacharias; it is first mentioned in Armenian sources in the history of Movses Khorenatsi, who explains this name as deriving from Sisak, the name of one of the descendants of the legendary Armenian progenitor Hayk. Strabo mentions a region of Armenia called Phaunitis, which some scholars read as *Saunitis and connect with Syunik. If Phaunitis is not to be identified with Syunik, then the earliest mention of the name in Greek sources is by Eusebius in the 4th century, who refers to it as Saunia. Later, in the 6th century, the Byzantine historian Procopius refers to the inhabitants of the province as Sounitai. In the Ravenna Cosmography (c. 700), Syunik is referred to in Latin as Siania Caucasorum. In Georgian sources, Syunik is typically called Sivnieti, while Arabic sources knew it as Sisajan, borrowed from Persian.

The ultimate etymology of the name Syunik is unknown. At first glance, it appears to be the plural of Siwni, the name of the ancient princely dynasty of Syunik (the noble house, like the province, is also alternatively called Sisakan). Historian Armen Petrosyan has suggested that Syunik is related to the name of the Urartian sun god Shivini/Siwini (itself a borrowing from the Hittites), noting the similarity between the names and the high number of sun-related placenames in the region. Robert H. Hewsen writes that Syunik is probably identical with the place name Ṣuluqū mentioned in Urartian cuneiform inscriptions.

Syunik was a big region in the east of historical Armenia. In the west and north-west, it bordered on the Ayrarat Province; in the east, the natural border between Syunik and Artsakh passed through the Hakari river (left inflow of the Aras). In the north-west, Syunik shared a border with lands situated in the direct neighborhood of Ganja, and in the south-west, it bordered on Nakhichevan (Vaspurakan Province). The north of Syunik comprised Gegharkunik and Sotk which lied on the coast of Lake Sevan. In the south, the territory of Syunik extended to the Aras River.

According to Ashkharhatsuyts in the 7th century, Syunik was divided into 12 administrative-territorial regions (gavars):

9. To the east from Ayrarat - between Yeraskh (Araks) and Artsakh - Syrunik has 12 regions: 1. Alijna, 2. Chaguk, 3. Vayots Dzor, 4. Gelakuni with the sea, 5. Sotk, 6. Agaghechk, 7. Tsgak, 8. Gaband, 9. Bagk or Balk, 10. Dzork, 11. Arevvik, 12. Kusakan. The province is known for such endemic plant species as myrtus, gereri (?) and grenade. It also has many mountainous areas.

— Anania Shirakatsi, Ashkharhatsuyts

Ptolemy refers to the Sotk region as Sodukena (from the ancient Greek Σοδουκην) in the following record: "The regions of Armenia at the junction of the rivers Euphrates, Kir ad Aras; here's the essence: Kotarzen – near the Moschian Mountains, above the so-called "heavenly creatures" (?), Tosarensk (?) and Otene – along the river Kir, Koltensk (?) – along the river Aras, and Sodukensk – below it; Sirekan and Sakasensk at the foot of Mounts Sirekan and Sakasensk".