The strange case of Tibetan thul ‘egg, testicle’

In a recent post on ‘water’ and ‘lip’ (https://stan.hypotheses.org/20) I identified a correspondence indicating PST *-ur:

OC *-ur, Bodo -əy, Lushai -ui, -Proto-Karen *-ej, WT *-u.

‘Egg’ would fit into that correspondence beautifully —the coda in the OC word is ambiguous for *-r—if it was not for a rare WT word for ‘egg’:

Written Tibetan	Boro (Bhat)	Lushai (Lorrain)	Proto-Karen (Luang.)	OC (B-S)	PST (tentative)
! thul ‘egg, testicle’	dəy ‘egg’	tui ‘egg’	Ɂdej B ‘egg’	tʰu[n] ‘egg’	#tʰur
chu ‘water’	dəy  ‘water, river’	tui ‘water’	thej A ‘water’	s.turʔ ‘river, water’	#s-turʔ
mchu ‘lip’	(gusu)təy ‘lip’	(not cognate)	n.a.	sə.dur ‘lip’	#m-tur

The expected rhyme correspondence for WT is -u, as shown by ‘water’ and ‘lip’. What is going on ?

Here is an idea. OC had an <r> infix that it shares with Austronesian and it would make sense if TB did, too. Some minimal pairs involving medial -r- and showing semantic alternations very much like Chinese can be found in TB languages:  medial -r- calls attention to the distributed character of objects or actions. I treat medial -r- as the <r> infix in the pairs below:

Written Burmese: pok ‘a drop (of liquid)’ : p<r>ok ‘speckled, spotted’

Chepang: pop ‘lungs’ : p<r>op ‘lungs’

Jingpo: phun31 ‘of lumps or pimples, to appear on the body’ : ph<r>un31 ‘pimples, lumps on the body; to appear on the body, of pimples or lumps’

Such pairs are never found with alveolar initials; Zev Handel has claimed that *tr- clusters do not reconstruct to PTB or even PST (Handel 2002). Another possibility exists: *tr clusters (including infixal *t<r>- clusters) existed in PST but merged with *t- in PTB (this would constitute a TB innovation).

There are no WT words of the shape CrVr, that is, with both medial -r- and final -r. In my first post to this blog (https://stan.hypotheses.org/11) I suggested that when that situation arose, for instance after the metathesis of preinitial -r, final -r dissimilated to -l. Supposing that a constraint on medial and coda r already existed in PST, a PST doublet involving a root *thur and the <r> infix would alternate *thur vs. *th<r>ul. By the changes described in my earlier posts, this doublet would evolve to PTB *thuy vs. *thul. In WT, *thuy would evolve to thu (chu if palatalized); but WT actually thul reflects PST *th<r>ul, the infixed variant.

References

Handel, Zev. 2002. Rethinking the medials of Old Chinese: Where are the r’s? Cahiers de Linguistique Asie Orientale 31.1:3-32.

Sagart, Laurent. 1993. L’infixe -r- en chinois archaique. Bulletin de la Société de Linguistique de Paris, Tome LXXXVIII, fascicule 1, pp. 261-293.

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