Publishing history:v1.0
v1.0: 29/04/26
sgor m. [s̪kɔɾ], gen. sgoir [s̪kɔɾʲ], in the sense ‘notch’ is derived from ON skor f. ‘idem’ by Alexander Cameron (in MacBain 1894a, 642), so also Craigie (1894, 164), Mackay (1897, 94: Ice. skor), Henderson (1910, 120), Bugge (1912, 304), Christiansen (1938, 4, 16 
Who cites Henderson (although Henderson’s p. 184 should be p. 120), and who (p. 16) refers to SG sgor as the name of a locality, whereas his informant in fact uses the word as an appellative (p. 4).
So also Stewart 2004, 413.
De Vries (1962) cites Henderson (although Henderson’s p. 112 should be p. 120) for SG sgor.
While potentially from ON skor, SG sgor in the sense ‘notch’ may be from Scots score (with a short, unlengthened vowel 
SND˄ gives Scots score [sko(ə)r], while The Online Scots Dictionary˄ gives [skoː(ə)r] and Jakobsen (1928, s.v. skor) [skōr], [skōər]. The vowel is etymologically short, but may lengthen phonetically before /r/ under the effects of the Scottish Vowel-Length Rule (SVLR), although lengthening before an epenthetic schwa seems unlikely; in consequence, for SND’s [sko(ə)r], we should perhaps read [sko(:)r], [skoər] (pers. comm. Pauline Graham). This does not necessarily provide a terminus ante quem for a Scottish Gaelic loan: while SVLR is thought to have been established over the course of the mid- to late 16th century (Aitken 2002, 130), ‘the further north from central Scotland you travel, the more there will be specific words which do not conform to the [Scottish Vowel-Length] rule’ (Millar 2007, 20).
ON skor > late OEng. skoru > MEng. scŏre > scōre, with lengthening of the stressed vowel in an open syllable during the 13th century (Brook 1975, 21).
Craigie (1894, 164) and Bugge (1912, 304) suggest Ir. scor ‘notch’ derives from ON skor; so also Marstrander (1915a, 64, 143), after Bugge, and on the basis that an Irish tradition of commemorating an important event by cutting a notch in the mantlepiece (referred to in Dinneen 1904, s.v. scor: scor a chur ’s an chlabhar) was borrowed from the Norse – but this is hardly proven. De Vries (1962) cites Bugge for OG [leg. Ir.] scor.
MacBain (1896; 1911) derives Ir. scór from Eng. score.
In addition to ‘notch, incision’, ON skor has the senses ‘cleft, mountain ledge’ (NO) and ‘canyon, gorge’ (NSL˄), and the Old Norse word may well be behind SG sgor in the sense ‘cleft’ (e.g. Sgor an Teine ‘the cleft of the fire (lightning)’, alias Sgor na Caillich ‘—of the old woman’ NB226461 (Cox 2002a, 365)) and Mx skor in the sense ‘rift’ (Kelly 1991; plural in the anglicised place-name The Skoryn (Marstrander 1932, 178)), 
In discussion, McDonald (2009, 403–04) cites Taylor’s (1968, 126) derivation of the Boreray (St Kilda) place-name SG Clesgor [sic] from ON *Klifsskor ‘(the) rift of the cliff’, with genitive of ON klif nt., but Clesgor is an Old Norse loan-name in Gaelic and does not establish whether ON skor was itself borrowed into Gaelic.
Cf. SG sgòr ‘hill’.