SeiTT (asker) Jun 6, 2012:

Onomatopoeia Many thanks, very helpful indeed.

If we compare غروچ and قروچه, in spite of the superficial differences, given that ق and غ have the same pronunciation, it would seem that they are essentially the same word.

What is particularly interesting to me is the pronunciation: while the pronunciation of the consonants is no problem, I note that Hossein gives a short O for the first two vowels, while the one-volume Āryānpur Progressive Persian-English Dictionary gives OO i.e. long U. But perhaps this is one of those things that varies from region to region? This is, of course, frequently encountered in onomatopoeias.

And, indeed, since the grinding of teeth is a consonantal sound, I suppose that, in a sense, the vowel part is a mere fill-in!