v. to decline, worsen
n. decline, worsening

Het mah Arnvid faal Staadnau, wen Haas denos mindin Kein do Galik, kolos rok ofaal dilos ahraan.
Here fell Arnvid the Unbound, whose Health declined after the War of Pines, in which he received a deadly wound.
(Word Wall for Haas, Drain Vitality)

To worsen in state or condition, to fail to improve.

May share root with denek ‘soil’ indicating something below or beneath.

Not 'decline' as in 'to decline an offer'.