The Old Norse form of the name was just Hinn (the suffix -øya meaning "the island" was added later). The large island is almost divided in two parts by the Gullesfjorden and Øksfjorden, and the old name is probably derived from an old verb with the meaning "cleave", "split", or "cut".[3]
Hinnøya is dissected by several fjords, and two very long ones, Gullesfjorden in the northeast and Øksfjorden in the southwest, almost sever the island in half. There is a five-kilometre-wide (3 mi) isthmus between innermost parts of the two fjords. Tjeldsundet sound divides Hinnøya from the mainland and from Tjeldøya; the narrow Raftsundet strait divides Hinnøya from Austvågøya and between Hinnøya and Andøya goes Risøyrenna strait. The island contains a mostly rugged and mountainous terrain, especially the southern part. There are also valleys and lakes, the largest lake is Storvatnet at 6,67 km2. The treeline lies close to 400 m above sea level, but varies from 250 m to nearly 500 m above sea level.
The best agricultural area is in the northeast, in Harstad and Kvæfjord Municipalities. The southern part is the location of Møysalen National Park, which includes the highest mountain on the island, the 1,262-metre (4,140 ft) tall Møysalen.[4] In the northwestern part of the island, near the village of Forfjord, there is a nature reserve containing a valley with forests and bogs, including the oldest pine trees in Norway, more than 700 years old.[5]
The climate of the southern coast of the island is warmer and wetter in winter than the northern coast. Harstad, situated on the northern part of Hinnøya, has all-time high 31.7 °C (89 °F) recorded July 2014, and record low −16.1 °C (3 °F) recorded in February 2010.
Eastern Hinnøya facing Tjeldsundet in April. The highest mountain is Strandtinden (1,076 m) on southeastern Hinnøya
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