Rhiw Llwyd is the name of an early medieval Wales lordship which was created in the Kingdom of Gwynedd in the 12th century for Tomas ap Rhodri ab Owain Gwynedd and his successors. The location of this lordship is not certain but it seems likely it refers to a hill of the same name (meaning in Welsh "grey slope") between Penmachno and Ysbyty Ifan in Gwynedd.