The Rune Axe of Grimnir is a runic two-handed axe. Wielded by Grombrindal, it is an impressive weapon that increases the wielder's strength.[1][2]
It is dedicated to Grimnir, and matches the description of the Ancestor God's weapon found in several sagas. Perhaps it is indeed Grimnir's axe, gifted by him to the White Dwarf.[1][2]