There are probably many potential idiomatic translations of this, so we stick with those most common in Welsh English: 'the thing I hate the most' or 'my pet hate'.

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)