Ústyrkjast

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

ústyrkjast

(t), v. refl. to grow infirm.

Possible runic inscription in Younger Futhark:ᚢᛋᛏᚢᚱᚴᛁᛅᛋᛏ