Undirrót

As defined by A Concise Dictionary of Old Icelandic (Geir Zoëga):

undirrót

f. origin prime cause of a thing.

Possible runic inscription in Younger Futhark:ᚢᚾᛏᛁᚱᚱᚢᛏ

Also available in related dictionaries:

This headword also appears in dictionaries of other languages closely related to Old Icelandic.

• Old Norse - Cleasby & Vigfusson Dictionary
• Old Norwegian - Johan Fritzner's Dictionary