So, I’ve been trying (once again) to read Harry Potter in Welsh, and the word oherwydd comes up a fair bit in the first chapter. The closest I can come to a translation for it is because - for which I learned achos. I get the gist of the sentences the word was used in, but I was wondering what the main difference was between the two words in practice.
According to Gareth King’s Modern Welsh (an invaluable resource for questions such as these), p. 321: achos and oherwydd are interchangeable when used for English ‘because’, oherwydd has the additional meaning of ‘because of’, whereas with achos, you need ‘o achos’ to make it equivalent to English ‘because of’. I guess ‘oherwydd’ already has the ‘o’, the old spelling being ‘o herwydd’
Also, I’d say oherwydd is used a little less often now, and sounds a little more flowery.
I agree with @louis .
And I agree with @aran too.
Note also the useful phrase o’r herwydd, meaning so = for that reason (i.e. just stated)
Doedd dim bwyd ar ôl, ac o’r herwydd aeth pawb adre.
There was no food left, so everyone went home
Oedd pawb wedi mynd adre o’r herwydd/felly doedd neb yn gofyn “Pa brechdanau sydd dach chi?”… ac eithrio morgrugyn…
According to Gareth King’s Modern Welsh (an invaluable resource for questions such as these), p. 321: achos
Page 314 in my copy. Earlier edition perhaps? Immensely useful book.