
As I've probably mentioned before, I strongly suspect Julius Pokorny and followers have lazily lumped Sanskrit kapúcchala 'tuft of hair from the back of the head' in with other evidence supposedly supporting Proto-Indo-European (PIE) *kaput 'head', all just to give the illusion that the evidence is more robust and geographically dispersed than it honestly is. It's also a lot easier in any bureaucracy, including in academia, to simply go with the flow and ne'er question the status quo. However in this case, I'm fortunately not the only one out there that thinks this smells fishy. I insist that this PIE root never existed and that there are only Western European reflexes of this 'head' word, all attributable to loans from the Aegean family during the 2nd millennium BCE and later, ie. from either Minoan *kaupada (> Greek κεφαλή) or Etruscan *kaupaθ (> Latin caput; indirectly into Germanic as *haubidaz prior to Grimm's Law, perhaps through Venetic).
Though I found one lead online stating that Mayrhofer once dared to analyse kapucchala into a pejorative prefix ka- plus puccha- 'tail' (Mayrhofer, Kurzgefaßtes etymologisches Wörterbuch des Altindischen [1956], p.157), I've just come across a curious entry in both Cologne Digital Sanskrit Dictionary and Capeller's Sanskrit-English Dictionary that identifies the syllable क ka alone as 'head'. This tickles me. Since I knew already that पुच्छ puccha meant 'tail', this implies that कपुच्छ ka-púccha-la- with diminutive -la- just means 'little head-tail', perfectly fitting for a tuft at the back of the head.
If the word can be explained purely in Sanskrit terms, a PIE origin would be woefully extravagant by comparison and then easily dismissed as bunk. The other spelling kaputsala would be just an alternative phonetically-faithful rendering and certainly adds nothing to the arguments of the **kaput camp until they can substantiate both **kaput and **śala-. Even the justification for this unmotivated segmentation of the word is lacking. It seems to be based on wishful thinking.[1]
That being said, now I'm having trouble confirming the source of the equation ka = 'head'. Is it attested somewhere directly? Or is this purely assumed by 19th-century Indicists attempting to etymologize Sanskrit vocabulary (in which case, an asterisked *ka is in order)? Oddly enough, there a few other words that strongly seem prefixed with this morpheme ka-: क-स्तम्भी kastambhī 'prop of a carriage-pole' (cf. स्तम्भ stambha 'post, pillar') and कं-धर kaṃdhara 'neck' (lit. 'head-bearer', cf. धर dhara 'supporting').
Rejecting PIE **kaput, what then is the etymology of Sanskrit क ka 'head'?
NOTES
[1] After posting this, I managed to discover one tantalizing lead that may help settle this issue (see Brugmann/Streitberg, Indogermanische Forschungen, v. 3 [1894], p.236) which I subsequently posted in my commentbox. If I'm reading the German correctly, it seems like the authors are admitting that kaputsala was caused by a more modern modification of kapucchala, based on an etymological whim.