v1.1
Publishing history:
v1.0: 01/10/24
v1.1: 07/05/25
fang f.
MacEachen (1842: gen. faing), MacLennan (1925: no genitive cited) and Dieckhoff (1932: no genitive cited) give masculine.
Lewis, North and West Sutherland, Wester Ross, Raasay and parts of Skye.
Cf. SGDS Items 394 fang, 395 (dat.) faing. Also, for Islay and Skye, see Holmer 1938, 164; for Kintyre, see Holmer 1962, 53; for East Perthshire, see Ó Murchú 1989, 340; for West Perthshire, see Ó Murchú 2022, 231; for Gairloch, see Wentworth 2003, s.v. fank; and for Lewis, see Borgstrøm 1940, 77, and Oftedal 1956, 88.
MacBain (1911) derives SG fang from Scots fank ‘a sheepfold, a walled or fenced pen for sheep; a sheep-shearing at a fank; a small cattle-fair, held at a fank’ (SND˄, s.v. 2fank); so MacLennan (1925), Borgstrøm (1940, 770) and Oftedal (1956, 88). Christiansen (1938, 5, 18) connects faing (which he mistakenly describes as the genitive of fang) with Scots fank or Norw. fang, fanga, but the verbal noun SG fangadh with ON fanga. Cox (1987 II, 109, No. 1340) supports a derivation from ON fang nt. ‘grasp, hold; embrace’ (not attested with the specific sense of ‘sheep-pen’), from the Old Norse verb fanga ‘to capture, imprison; get hold of ’ (NO), 
So also Cox 1991, 493; 1992, 138.
ON fang would be expected to yield SG [fãŋɡ̊] in the first instance, cf. the Lewis place-names ON *Langavatn ‘(the) long loch’ > SG Langabhat [ˈɫ̪ɑ̃ŋɡ̊ə ˌvaʰt̪]; ON *Mangarastað acc. ‘(the) farm of the pedlar’ > SG Mangarstadh [ˈmãŋɡ̊ə ˌʂʈaɣ]; ON *Tunga ‘(the) tongue’ > SG Tunga [ˈt̪ʰũŋɡ̊ə]; ON *Vangssætr ‘(the) sheiling of the meadow’ > SG Ungaiseadar [ˈũũŋɡ̊ə ˌ ʃad̪̥əɾ]; although in Lewis the loan-word langa [ˈɫ̪ɑ̃ɣə] ‘ling’ (< ON langa f., s.v. langa) has developed along the lines of native SG (Lewis) teanga [ˈtʲʰɛ̃ɣə] ‘tongue’ (OG tengae) (Cox 2022, 149–50).
Scots fank [faŋk] might also be expected to yield SG [fãŋɡ̊] in the first instance, cf. Scots anker (anchor) > SG (Easter Ross) angar /ɑŋɡər/ (Watson 2022, 101), s.v. acaire); Scots blink > SG bliong [blũ̟ŋɡ] etc. ‘lythe’ (Faclan bhon t-Sluagh˄), s.v. bliong); Scots brank > SG brang [b̥ɾãŋɡ̊] ‘a horse’s halter’; and (with the development in Gaelic of a palatalised velar cluster, with subsequent diphthongisation of the preceding vowel) Scots bink (benk) > SG being [b̥ẽĩŋʲɡ̊ʲ] ‘bench’ (s.v. being); Scots thank > SG taing [t̪ʰãĩŋʲɡ̊ʲ] ‘thanks’; Scots stank > SG staing [s̪t̪ãĩŋʲɡ̊ʲ] ‘ditch; difficulty’ (s.v. stang) (although some recent loans show Scots/Eng. nk [ŋk] yielding SG nc [ŋ̊k] /ɴk/: Scots/Eng. bank > SG banc(a) [ˈb̥ãŋ̊k(ə)]; Scots/Eng. tank > SG tanc(a) [ˈt̪ʰãŋ̊k(ə)]; Scots funk > SG func [ˈfũŋ̊k]; 
Cf. Oftedal 1956, 140: /fũNk/. The Scottish Gaelic word func is usually used with a negative verb to mean ‘nothing’ and probably derives from Scots funk, a variant of fung, in the sense ‘blow, cuff, kick; throw, toss’ (SND˄, s.v. 1fung).
Doublets with both unpalatalised and palatalised forms are also found: Scots banket > SG bangaid [ˈb̥ãŋɡ̊ad̥ʲ] ~ baingeaid [ˈb̥ãĩŋʲɡ̊ʲad̥ʲ] ‘banquet’; Scots Frank ⇒ SG Frangach [ˈfɾãŋɡ̊əx] etc. ~ Fraingeach [ˈfɾãĩŋʲɡ̊ʲəx] etc. ‘French’.
Warrack (1911) gives ‘a trap, “a tight place”’ and EDDo˄ ‘a trap, “a fix, a tight place”’.
In the case of SG trang, the alternative is to date its borrowing from Scots to before the simplification of Scots /ŋɡ/, which took place by the late 14th century at least (cf. Johnston 1997, 101).
SND˄’s reference to Ir. fang is problematic: it seems to occur only in O’Reilly’s (1817; 1864: ‘pound, prison for cattle’) Irish dictionary, where it may well have been adopted from Shaw’s (1780), Mac Farlan’s (1795) and/or MacFarlane’s (1815) Scottish Gaelic dictionaries.
HSS 1828 cites O’Reilly’s Ir. fang.
It seems probable, then, that either Scots fang or Scots fank (as a variant of fang, cf. Scots fangle ~ fankle 
Frequentative forms of fang ~ fank, respectively (SND˄).
Cf. also the Kintyre form [faŋk], otherwise [fɛŋg], recorded by Holmer (1962, 53, 72).
See, for example, Hunter 2019, 49.
Derivatives: A number of open compounds are found, e.g. fang-chaorach ‘sheep-pen’ (LASID IV, 260, s.v. fainc, Lewis), fang-glacaidh ‘gripping-pen’ (Faclan bhon t-Sluagh˄: North Uist, Skye, Mull), fang ghlacaidh (ibid.: Gairloch), faing-ghlacaidh ‘idem’, faing an dupi/faing-dhupaidh [sic] ‘dipping-pen’ and faing (togail) nan uan ‘lamb-separating pen’ (ibid.: Lewis); also the verbs fangaim (Shaw 1780: ‘I impound, enclose in a fold’), i.e. fang (Armstrong 1825: ‘to drive into a fold or pen’; Faclan bhon t-Sluagh˄: ‘to put an animal into a position where it can be caught’, Harris) and fangaich (MacFarlane 1815: ‘to put in a fold’; Armstrong: ‘to fold, gather in a fold or pen’; HSS 1828: ‘to enclose, put into a fold’; MacLeod and Dewar 1839: ‘idem’; MacEachen 1842: ‘idem’; Dwelly 1911: ‘to enclose, pen, fold’; MacLennan 1925: ‘to put into a fold’; AFB˄: ‘to enclose, pen’); the verbal nouns fangadh (Mac Farlan 1795: ‘to drive to a fold’ [sic]; HSS 1828: ‘penning, enclosing in a sheep fold’; MacLeod and Dewar 1839: ‘idem’; Christiansen 1938, 18: fangadh, 25: fangach [sic] ‘round up sheep’, Lewis), fangachadh (Armstrong 1825: ‘driving into a fold, a penning of cattle’; HSS 1828: ‘penning, enclosing in a sheep fold’; MacLeod and Dewar 1839: ‘idem’; MacEachen 1842; Dwelly 1911: ‘penning of cattle or sheep, driving into a fold’; AFB˄: ‘penning, driving into a cattle fold’) and fangaich (Faclan bhon t-Sluagh˄: ‘fanking, enclosing animals in a fank’, Arran); and the adjective fangach (Dwelly 1911: ‘full of folds or pens etc.’; AFB˄: ‘pertaining to or abounding in fanks etc.’).