Yggdrasil (Old Norse 'Yggr's horse') is a cosmic tree from which Odin sacrificed himself, and which connects the Nine worlds. 19th century scholar Jakob Grimm connects the name Irmin with Old Norse terms like iörmungrund ("great ground", i.e. the Earth) or iörmungandr ("great snake", i.e. the Midgard serpent).[2]