Rhydderch \rh(y)-dder-ch, rhydd(e)-rch\ as a boy's name is of Welsh origin, and the meaning of Rhydderch is "reddish-brown". Rather common name in the Middle Ages. See also Roderick.
For more information, see also the related name Broderick.
Baby names that sound like Rhydderch are Roderich, Rodderick and Rhoderick.