A or an horrendous

With my pronunciation, A.

If someone doesn't say the "H" then it would be "An 'orrendous."

I don't know if there are dialects that don't say the H in horrendous. (I don't say it in "historic.")

I went a top English School and we were taught to write ...an horrendous... but just try running THAT past the (american) spell checker in Microsoft Office Word.... you can't!

I think it is simply a matter of what 9new deems preferable.

If an expression is repeated often enough, it becomes 'correct'. Today, it is okay to split an infinitive ... apparently. The word 'whom' is beginning to fall from favour. People now write 'to' people, which is still incorrect. 'An horrendous' is now in limbo. It is often said and not questioned, but most of us are left to wonder ... I still use 'an horrendous' as it trips off the tongue

There is an horrendous football game today.

An Horrendous

Both versions are 'correct'.

It's a matter of personal preference.

In British or Australian English "an" is preferred and spoken. "A horrendous" sounds to my ear awkward and vulgar. If in Australia one uses "a" you'd be considered uneducated, regardless of the supposed formal rules allowing the usage.