The meaning of the Welsh placename is uncertain, although the church is now dedicated to St. Clydaï, an alleged daughter of Brychan.

[3] During the early Middle Ages, the settlement was the site of Llangeneu ('St Ceneus'),[4] which was accounted one of the seven principal sees of Dyfed despite having no endowment of land.

[7] Josiah Thomas Jones (1799-1873), republican and Welsh nationalist, was born at CwmHir Farm, Clydau.

He went on to publish many books and established several newspapers in English and Welsh, including the Aberdare Times.

Although the settlement of Clydau is tiny, the community is large, encompassing several other settlements and/or parishes including Bwlchygroes, Star, Tegryn, West Cilrhedyn and a large number of scattered farms.