Publishing history:v2.0
v1.0: 01/10/24
v1.1: 04/03/25
v2.0: 19/03/25: Discussion on The Storr and The Old Man of Storr placed under stòrag.
starrag f. [ˈs̪t̪ɑɍaɡ̊], 
Cf. /sdaRag/ (AFB˄). The word is recorded as stearrag, with a palatalised initial cluster, in a short list of bird names drawn up by a nine-year-old informant from Scalpay (Faclan bhon t-Sluagh˄, q.v.), but this is probably for starrag – the list contains several spelling errors – and may have been influenced by SG steàrnag ‘tern’.
Fergusson 1886, 46: Harris; so Forbes 1905, 37, and Dwelly 1911; Faclan bhon t-Sluagh˄: Lewis, North Uist; AFB˄: Lewis, Harris, Scalpay, Tiree.
Comparing the sense ‘wry-neck, stiff-neck’ (MacLennan 1925 
Who compares MHGerm. starren ‘to become fixed’ and Germ. starr ‘stiff, stiff-necked’.
Although citing ON star (leg. stari), starri m. ‘starling’.
A semantically more suitable solution might be a loan-blend from Scots sture, stare etc. [stu:r], [stø:r], [ste:r], [sti:r] in the sense ‘(of the voice) deep and hoarse, harsh, rough’ (SND˄, < ON stórr ‘big’), with reference to the bird’s grating caw. While the Scots word usually has a long vowel, it is recorded as [stur] with a short vowel in Orkney (Marwick 1929, s.v. stoor adj., and p. xli 
Cf. Scots (Orkney) sooken [´sukən] < ON sókn f. ‘district’ (ibid.)
One might also compare SG stàrr vb ‘to shove, dash’, the verbal noun starradh m., and the compounds cnap-starra(idh) ‘obstruction’ and stàrr-fhiacail(l) ‘tusk, protruding tooth’, also starrag ‘protruding tooth, obstruction’; cf. Ir. starr f. ‘prominence, projection; tusk; stumble’ (Ó Dónaill 1977; var. storr (Dinneen 1947)) and the derivatives starraic, starraicín, starrán, starróg, starrfhiacail and, in place-names, storral (cf. Joyce 1893 II, 38–39; Tempan 2010–20˄, s.nn. Barrclashcame North-West Top, Mullaghasturrakeen, Slievenalecka, Sturrakeen, The Sturrall). While Joyce refers to a root stur (based on anglicised forms of place-names), Tempan (ibid., s.v. The Sturrall; 2007˄) takes Ir. starr, storr to be from Ir. tor ‘pinnacle, rock-tower’ (EG tor ‘tower, fortified building’, < Lat. turris (eDIL˄)), with prothetic s-, 
For examples of prothetic s- in Irish, see Ó Curnáin 2007 I, 258.
SG tòrr, rather than *tor, may be the result of conflation with SG tàrr ‘belly, stomach etc.’ (EG tarr).
In summary, the etymology of SG starrag is uncertain: it might be a loan-blend from ON starr adj. (or starri m.) or Scots sture, stare, or it might be a derivative of SG *stàrr, a by-form of EG s-tor or, doubtfully, EG sparr; or it might be from one source but have been influenced by another.