An Irminsul (Old Saxon, probably "great/mighty pillar" or "arising pillar") was a sacral pillar-like object attested as playing an important role in the Germanic paganism of the Saxon people. The oldest chronicle describing an Irminsul refers to it as a tree trunk erected in the open air. The purpose of the Irminsuls and the implications thereof have been the subject of considerable scholarly discourse and speculation for hundreds of years.
A Germanic god Irmin, inferred from the name Irminsul and the tribal name Irminones, is sometimes presumed to have been the national god or demi-god of the Saxons. It has been suggested that Irmin was more probably an aspect or epithet of some other deity – most likely Wodan (Odin). Irmin might also have been an epithet of the god Ziu (Tyr) in early Germanic times, only later transferred to Odin, as certain scholars subscribe to the idea that Odin replaced Tyr as the chief Germanic deity at the onset of the Migration Period. This was the favored view of early 20th century Nordicist writers, but it is not generally considered likely in modern times.
The Old Norse form of Irmin is Jörmunr, which just like Yggr was one of the names of Odin. Yggdrasil ("Yggr's horse") was the yew or ash tree from which Odin sacrificed himself, and which connected the nine worlds. 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).