From Middle English rewe, reowe, from Old English hrēow ("sorrow, regret, penitence, repentance, penance"), from Proto-West Germanic *hreuwu ("pain, sadness, regret, repentance").
From Middle English rewen, ruwen, ruen, reowen, from Old English hrēowan, perhaps influenced by Old Norse hryggja, from Proto-Germanic *hrewwaną.