"Fy nghas beth"

Translation: My pet hate

[JamesTWils]

So, is there some superlative here? Is nghas a verbal adjective of some sort? Is it derived from casau in some regular way that I could derive a similar superlative adjective from some other verb?

[ibisc]

It might be easier to think of these as idioms:

• Fy nghas beth yw... (My pet hate is...; The thing I hate most is...)

• Fy hoff beth yw... (My favourite thing is ...)

cas and hoff are two of a small number of adjectives which can have slightly different meanings when used before or after the noun. Putting cas and hoff after a noun gives us:

• y ci cas; y gath gas (the nasty dog; the nasty cat)

• ffrind hoff (a dear friend) (not such a common usage, but you do meet it sometimes)

[Beckyhartman117]

I have never heard of a pet hate before

[JamesTWils]

As Stardecki says above, in the United States, we would definitely only say "pet peeve."

[ibisc]

'pet peeve' is another accepted translation here.