rue 1 
(r)
(r)v. rued, ru·ing, rues
v. tr.
To feel regret, remorse, or sorrow for: “I never rued a day in my life like the one I rued when I left that old mother of mine” (Flannery O'Connor).
v. intr.
To feel regret, remorse, or sorrow.
n.
Sorrow; regret: “I ... won her from various rivals, who ... went away, one may say, full of rue” (Brian Doyle).
[Middle English rewen, partly from Old English hrēowan, to distress, vex, and partly from hrēowian, to repent; akin to Dutch rouwen, to mourn, and Old Norse hrjá, to afflict, all from Germanic *hrewan, to be sad, make sad, of unknown origin.]
ruer n.