Fyrstr

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

fyrstr

a. superl. the first, foremost; hinn fyrra hlut vetrar, in the early part of the winter; hit fyrra sumar, the summer before last; yðrir fyrri frændr, your ancestors; verða fyrri til e-s, at e-u, to be the first to do a thing; eigi fellr tré við hit fyrsta högg, a tree does not fall at the first blow.

Possible runic inscription in Younger Futhark:ᚠᚢᚱᛋᛏᚱ