v2.1
Publishing history:
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.
v2.1: 22/10/25: Examples of starr- etc. in Irish place-names, especially in Donegal, expanded.
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, see Joyce 1912 II, 38–39: storral; Tempan 2010–20˄, s.nn. Barrclashcame North-West Top (Starraicín na gCaor, Mayo), Mullaghasturrakeen (Tyrone), Slievenalecka (An Starraicín, Kerry), Sturrakeen (Tipperary), The Sturrall (Donegal); and Watson 2019, 204, s.nn. An Stairrál, An Stairrín, An Starraicín, An Starral etc. (Donegal). 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. (For further discussion and further examples of prothetic s- in the Gaelic languages, see O’Rahilly 1927, 24–29: 27–29; Risk 1970, 628; Gleasure 1973, 190–91; Clancy 1992.)
SG tòrr (rather than *tor) from EG tor may be the result of conflation with SG tàrr ‘belly, stomach etc.’ (EG tarr).
Alternatively, Ir. starr and SG stàrr might just represent a by-form of EG sparr ‘spar, beam, rafter; stake, spike, nail; gate of a town or city, fortification’ (eDIL˄), perhaps under the influence of EG tor (cf. the derivative EG sparraḋ m. ‘fastening, nailing’), but, apart from HSS (1828) noting that SG stàrr vb means the same as SG spàrr vb, i.e. ‘to drive, as a nail or wedge; induce by force; fix, nail; thrust; inculcate’ (s.v. spàrr), there is no evidence for such a development.
In summary, the etymology of SG starrag is uncertain: it might be a loan-blend from ON starr adj. (or starri m.), less likely from Scots sture, stare; or it might be a derivative of SG stàrr ‘to shove, dash’, less likely a by-form of EG s-tor or of EG sparr. It might be from one source but have been influenced by another.