As a corollary to my posting regarding the dual and Sanskrit dvau, tau and Old Norse tvau, thau, I would like to make mention of another observation:
The word for "eight" is as.tau in classical Sanskrit and is ahtau in Gothic. This suggests that its final element was an u-diphthong, although I believe Vedic has rather as.ta: without u-diphthong. But what is interesting to me is that I seem to remember reading somewhere (I don't recall where) that Avestan had some word such as asta- (asto: if it were a masculine o-stem?) or similar with a meaning that could be related to the image of the four fingers of the hand held together -- a meaning something like "spearhead" or "palm (of the hand)" or some other meaning that I recall suggested that it could have been used as an indicator of the shape of the four fingers of the hand held together minus the thumb. This would suggest that two of those "spearheads" or whatever they were, of four fingers each, would make
"eight". This suggests that the origin of *ok'to:/ok'to:u might in fact be an old dual. Since Gothic unequivocally has -au in ahtau, if *ok'to:u is an old dual, it suggests that the ending *-o:u (Sanskrit -au) is original, and that this may be the regular dual ending of o-stems -- therefore Sanskrit -au would actually have its origin as a long u-diphthong, presumably *-o:u.
Does anybody have any opinions or insights about this idea? It was a long time ago that I came across that Avestan word, but I have a distinct memory of it being suggested as the origin of *ok'to:(u), unless my memory is faulty.
Andrew Jarrette