There’s a village near where I live called Betws-y-Coed [ˈbɛtʊs ə ˈkɔɨd], which means ‘prayer house in the wood’. I knew the meaning of the name, but hadn’t considered where the word betws might come from. Last night a friend told me that it comes from an English word ‘bead house’, meaning a prayer house or oratory.
Wikipedia agress with this saying the word Betws or Bettws comes from the Old English bed-hus (house of prayer, oratory). The name was first recorded as ‘Betus’ in 1254.
According to this Old English Dictionary the Old English word bed means ‘prayer, supplication; religious ordinance, service’, hús means ‘house; temple, tabernacle; dwelling-place; inn; household; family, race’, and gebédhús is a house of prayer or oratory.
Apparently the Welsh words bacws (bakery) and warws (warehouse) contain the same hús root. I can’t find confirmation of this, but it sounds plausible. I guessed that these words came from English, but hadn’t made the connection with Betws before.
They must have been borrowed before the Great Vowel Shift which started during the 14th century. Before then house or hús was pronounced /hu:s/, as it still is in northern English and Scots. The /haus/ pronunciation emerged during the 18th century.