Ablaut in the context of "Indo-European ablaut"

The roots of the reconstructed Proto-Indo-European language (PIE) are basic parts of words to carry a lexical meaning, so-called morphemes. PIE roots usually have verbal meaning like "to eat" or "to run". Roots never occurred alone in the language. Complete inflected verbs, nouns, and adjectives were formed by adding further morphemes to a root and potentially changing the root's vowel in a process called ablaut.

A root consists of a central vowel that is preceded and followed by at least one consonant each. A number of rules have been determined to specify which consonants can occur together, and in which order. The modern understanding of these rules is that the consonants with the highest sonority (*l, *r, *y, *n) are nearest to the vowel, and the ones with the lowest sonority such as plosives are furthest away. There are some exceptions to these rules such as thorn clusters.

Erilaz or Erilaʀ is a Migration period Proto-Norse word attested on various Elder Futhark inscriptions, which has often been interpreted to mean "magician" or "rune master", i.e., one who is capable of writing runes to magical effect. However, as Mees has shown, the word is an ablaut variant of earl, and is also thought to be linguistically related to the name of the tribe of the Heruli, so it is probably merely an old Germanic military title (see etymology below).