ruth.

From Middle English ruthe, reuthe, reuþe, reowthe, rewthe (“compassion, pity, sympathy; mercy; grief, sorrow; cause or event of pity or sorrow; lamentation; calamity, trouble; distress; regret, remorse; cruelty, ill treatment”), from reu, reuen (“to feel compassion or pity; to regret, rue; etc.”) + -th, -the (suffix denoting a condition, quality, state of being, etc.), possibly influenced by an early Scandinavian language (compare Old Norse hrygð, hryggð (“affliction, grief, sorrow, ruth”), from the Proto-Germanic word indicated below). Reuen is derived from Old English hrēowan (“to grieve; to regret, rue; to repent”), from Proto-West Germanic *hreuwan (“to cause pain; to regret”), from Proto-Germanic *hrewwaną (“to cause regret, rue; to feel sorrow, grieve”); further etymology uncertain, possibly from Proto-Indo-European *krew(H)-, possibly related to Proto-Indo-European *krewh₂- (“blood”) and *krows- (“to fall, beat, break, bruise”). By surface analysis, rue (“to regret; etc.”) + -th (suffix forming abstract nouns from verbs).