From Middle English roo, ro, from Old English rō, rōw (“quietness, quiet, rest”), from Proto-Germanic *rōō (“quiet, rest”), from Proto-Indo-European *h₁reh₁- (“to rest; quiet”). Cognate with Scots ro, ruve (“peace, repose”), German Ruhe (“rest, peace, tranquility”), Danish, Norwegian and Swedish ro (“rest, peace, tranquility”), Icelandic ró (“tranquility, quietness”).