PIE *plōtus etymology

I'm sorry for the back and forth about this one. I was working off of the AHD of IE Roots (http://web.archive.org/web/20080627204039/http://www.bartleby.com/61/roots/IE415.html) section I.6. which lists the the lengthened o-grade of *pleu- as *plō(u)- (or *plō(w)-, as the case may be). It seems very convenient of them just to list the u/w as optional, but do you think that this is a fair explanation, particularly if we list it as *plō(w}- + -*tus?

The problem is that there is no established sound change that would turn -ōw- into -ō-. -ōw- was allowed as a diphthong in Proto-Indo-European, just compare *gʷṓws (“cow”). So the change of -ōw- to -ō- must be accounted for somehow. Furthermore, the Germanic form does not necessarily need to reflect *plōtus. The -ō- could also originate from -eh₂- or -eh₃-. In fact, M Philippa's etymological dictionary of Dutch (which I've found to be very reliable over time) mentions a root *pleh₃- as a possible source of the Germanic words.

Ok, thanks for the input. Hopefully others will try to figure that out then. I wonder then why the AHD of IE Roots would allow that etymology in then? I had always understood it to be very reliable. Also, thank you for helping me in these early days of my Wiktionary editing.

Etymological dictionaries are often collections of information from various sources. They don't necessarily do any in-depth researching themselves, and may not have the know-how to judge them all. It's also possible that they just made mistakes or missed things, though. They're still human...

Kroonen gives -ōw- to -ō- as regular before a hiatus. I can go through and list some examples if you want.

Confusingly, he lists the Pre-Germanic form of *flōduz as *ploh₃tús, but states it is derived from the root of *flōaną, which he gives as *plōw-, as necessary for related *flawją (“ship”) and *flaumaz (“stream”). Maybe it's a middle ground of *pleh₃-u-?

For Germanic, that might indeed apply, yes. But this is a PIE reconstruction, and I doubt there was a law for the same there.

Yeah, sorry. It's a Germanic development, I should have specified.