1) English boy name 2) Glacier of Greenland 3) Hellhound of Norse mythology 4) Impact crater on Mars 
Watchdog of Hel; slays, and is slain by, Tyr at Ragnarok.
In Norse mythology, Garm is a hound which stands in front of Hel's home and snarls with jaws dripping blood at the pilgrims from the upper world.The Garm was a Norwegian torpedo boat of 540 tons displacement launched in 1913. The Garm had a top speed of 27 knots and carried a complement of 76. She was armed with six 3 inch guns and three 18 inch torpedo tubes.