This speculation, regardless of its plausibility, is devoted to Yael! Yael draws attention to a peculiar usage of the word shan by dPal-sprul in his account of the ordeal that Thogs-med underwent for the sake of directly encountering Maitreya, the future Buddha. The pertinent line reads: yang lam kha zhig na brag ri chen po dgung la reg pa zhig gi drung na mi zhig gis bya sgro zhig chu nang du shan nas brag de la byab cing ’dug. Yael assumes that the meaning of shan in the given context could be something like “dipped.” But what could be its etymology?
Honestly, I have no idea about the etymology of shan in any given context and so I have no choice but to speculate. For that, I would like to consider several words (that contain the syllable shan), the meanings of which seem more or less clear. I shall, however, exclude shan pa (or gshan pa) “butcher” or “hangman,” which seems to be cognates with gshed ma (“executioner” or “hangman”). See Jäschke 1881: s.vv. shan pa & gshed ma.
For the present purpose, I would like to consider five (groups of) words containing shan. First, we have a group of words in which shan clearly means an “(iron) hoop” as in lcags shan (or lcags shan brgyab), or, “(metal) rim” as in sga shan (“(metal) rim/fringe of a saddle”), or, “(silver inner) lining” (dngul shan) of a bowl as in dngul gyi kha shan, dngul shan ma (i.e. dngul shan g.yogs pa’i phor pa), and dngul shan brgyab. Here shan seems to mean a kind of “binding,” and shan brgyab “to bind or encircle with or as with hoops.” Second, what about shan in shan sbyar (e.g. skad gnyis shan sbyar)? Perhaps shan sbyar ba (as a verb) means “to bind or join (e.g. two semi-cylindrical parts) by means of hoops.” Interestingly shan sbyar ba is very much similar to lto sbyar ba (used, for instance, by Mi-pham in his commentary on the Madhyamakālaṃkāra). Second, what about shan in shan ’byed (i.e. dkar nag shan ’byed) and la shan dbye ba? It seems to be the opposite of shan sbyar ba, and thus means “split or separate” and “to differentiate/distinguish.” That is, as if taking the components of a barrel asunder by dismantling its metal hoops. Fourth, what about shan in shan zhugs pa? We know that in this context shan means “influence,” and perhaps etymologically “influence” means something that infiltrates (zhugs) into something (i.e. a barrel) through the gaps in between its metal hoops. Fifth, why is a boat called gru shan (cf. gru shan pa, gru shan gtong mkhan “boatman”)? Perhaps, gru shan is a “watertight vassel.” In all of these, shan seems to have something to do with “tightening” (also “water-tightening”) or “toughening.”
Finally, what could shan in bya sgro zhig chu nang du shan nas really mean? Perhaps here, too, the process of soaking or dipping in water presupposes a process of “tightening” or “toughening”? In the case of wooden barrels encircled with iron hoops, soaking in water may surely have a “tightening” effect. Perhaps it was believed that soaking or dipping feather in water made it more stiff and hence more effective in chiseling away a mountain towering in the sky? I wish I knew!