A grough is a natural channel or firm place in a peat moor:
How do you say it?
Does it rhyme with grow, cow, zoo, lough, or saw?
It's said gruff, as a matter of fact.
But how on earth anyone's supposed to know that I can't imagine.
Word Not To Use Today: grough. This is a new word - well, it's from the 1900s, anyway - so there's really no excuse for the impossible spelling. The word might come from an obsolete spelling of gruff in its obsolete meaning of a bit of rough terrain.
But wherever it originated, the people who coined it were far too busy showing off to be a help to anybody.