What is "elcmar"

In Irish mythology, Elcmar or Ecmar (modern spelling: Ealcmhar) was the husband of Boann and belonged to the semi-divine race the Tuatha de Danann, the people of Danu. It has been suggested that he is Nuada under another name, or that his name is an epithet for Nechtan the river god. At first glance he appears to be associated horses but there is also a school of thought that says his name means The Evil One.