We learned it as “sometimes Y and W “
Turns out there’s a perfectly good scrabble word “cwm” (pronounced “koom”)
That’s Welsh.
As is ‘crwth,’ another Welsh word, I believe.
cwm is the Welsh word for "valley" as part of a place name. The leading "aber" indicates the mouth of a river. Abertawe, Aberystwyth. Upstream from Aberystwyth along the river Ystwyth (Afon Ystwyth) is a small valley, Cwmystwyth with a few homes. My friends Meredydd Evans and his with Phyllis Kinney lived there. I last visited in 1999.