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buthaigear m. [ˈb̥u̟-iɡ̊ʲəɾ], [ˈb̥u-iɡ̊ʲəɾ], gen. buthaigeir -[əɾʲ], ‘puffin, Fratercula arctica’. There are four main forms of this word (A–D, below), each with its own variants and/or erroneous spellings: 
On Martin’s form bowger, Coates remarks (1988, 10) that ‘[t]he Gaelic dictionaries have invented some spellings for it like bugaire, budhaigir, budhaid, buthraigear, buigire ... which appear to indicate at least two pronunciation traditions, one with /k/ and one with /k'/, as well as numerous other points of variety’, which perhaps unintentionally implies the spellings are not based on spoken forms. The velar stops are phonemically /ɡ/ and /ɡ´/, not /k/ and /k´/.
A. bugair, buigir; bùgair, bùigir
A 1. bugair, bùgair
(i) bowger (Martin 1698, 91: ‘they use likewise the flesh of a fowl called by them bowger’, 94, 108), bouger (Buchan 1727, 21), bougir (Macaulay 1764, 153) and ’m boucier (Ross c. 1890, which consists of the typescript of a manuscript) are associated specifically with St Kilda; as essentially Scots orthographic forms, it is not clear whether the original Gaelic forms had short or long stressed vowels. Ross’s form is probably a misreading of an original *’m bouger (with aphaerisis of the Gaelic masculine singular article). As part of a concluding list, Ross also notes ‘puffin – bo’, but here the word seems to have been left unfinished by the typist, perhaps with a view to confirming the manuscript form, but never completed.
McDonald (2009, 347) takes Ross’s bo to be intentional.
(ii) bugair (Dwelly 1911).
(iii) buthgair m. (An Stòr-Dàta 1993), which, via an association with SG bùth [b̥u̟ː], [b̥uː] ‘shop’, may intend bùgair.
A 2. buigir, bùigir
(i) buigeir (Henderson 1910, 124); and
(ii) bòigear (MacBain 1896; Dwelly), boigear (Forbes 1905, 322).
B. bugaire, buigire; bùgaire, bùigire
B 1. bugaire, bùgaire
This form is found as bugaire in Forbes (ibid.) and Faclan bhon t-Sluagh˄ (for Harris).
B 2. buigire, bùigire
(i) buigire [bŭėgʹ-ėr-ȧ] (McAlpine 1832: 
Typeset out of alphabetical order after bucull.
(ii) bùigire (MacLennan 1925, s.v. budhaigir; Faclan bhon t-Sluagh˄: Harris, and [bu̟:ɡʹəɾə], Skye).
C. buthaigear, buthaigir
(with /V̄/ > /V-V/ and hiatus indicated by a digraph: th or dh)
C 1. buthaigear
(with a non-palatalised final)
buthaigear (Henderson ibid.: Barra and Harris; Faclan bhon t-Sluagh˄, Skye).
C 2. buthaigir
(with a palatalised final)
(i) budhaigir (HSS 1828; Forbes ibid.; Dwelly; MacBain; MacLennan: [boo’ugir]).
(ii) buthaigir (AFB˄: /bu.ɪgʲɪrʲ/).
(iii) buthaigre (Dwelly; An Stòr-Dàta 1993; AFB˄: f. /bu.ɪgʲrʲə/, Lewis, Harris and Skye), with metathesis.
C 3. (with epenthetic r)
buthraigear (Forbes ibid.; Henderson ibid.: Barra and Harris).
D. buthaid
(The ending here is perhaps formed on the analogy of the bird name pioghaid /pi.adʲ/ ‘magpie’, cf. also aghaid /a.adʲ/ ‘idem’ and ullaid /uLadʲ/ ‘owl’ (AFB˄).)
(with hiatus indicated by a digraph: th, dh, gh)
(i) buthaid (Dwelly; Faclan bhon t-Sluagh˄: South Uist, Lewis, Skye; AFB˄: /bu.ɪdʲ/, South Uist, Harris, Lewis, Skye).
(ii) budhaid (MacLennan).
(iii) bughaid (An Stòr-Dàta 1993; Faclan bhon t-Sluagh˄: Lewis).
(iv) bughaide f. (An Stòr-Dàta 1993), apparently a normalised genitive form of (i)–(iii).
(v) bùide (CG II, 335: buite, St Kilda; 
So also Dwelly.
(vi) puthaid (AFB˄: /pu.adʲ/, North Uist, Lewis, Skye), with /p/ ~ /b/ alternation.
(vii) bugaid (Faclan bhon t-Sluagh˄: Lewis 
One entry gives ‘puffin’, another quotes rinn e bugaid dheth ‘I killed it outright’ and tha e na bhugaid ann a sud ‘it’s lying stone dead there’. Here, bugaid may be based on Scots bouk ‘carcase’ (SND˄, s.v. 2bouk), or may be a loan from MScots boukit adj. ‘of large bulk’ (DOST˄, s.v.), in the sense ‘dead weight’.
(viii) buthaig f. (An Stòr-Dàta 1993), also budhaig (Cunningham 1990, 137), perhaps a normalised dative form of *buthag etc., with its ending based on the suffix -ag, commonly found in bird names, e.g. buidheag ‘yellow hammer’, feannag ‘crow’, curracag ‘lapwing’, or perhaps simply buthaid adapted to buthaig under the influence of such names. Alternatively, it may simply be a truncated form of buthaigear etc.
Mackenzie (1911, 53) suggests buigire means ‘damp fellow’, based on SG buige in the sense ‘dampness, moistness’, but this assumes an original short stressed vowel and seems unlikely to have generated either forms with long stressed vowels or those under (C).
MacBain cross-references bòigear to budhaigir, under which he suggests that budhaigir, buigire and Scots bowger, bouger are (≈) ‘somehow from ON bugr m. “curve”: i.e. “bent-bill?”’. Henderson (ibid.) argues that the form bugaire confirms MacBain’s derivation. Problematically, ON g is a velar fricative in the word bugr. Sommerfelt (1952b, 375), however, takes (C) buthaigear etc. as the primary form, deriving it from an unattested ON *bugakeri, consisting of (?a compound form of) bugr + keri ‘cock, male bird’, as found in ON rjúpkeri ‘cock ptarmigan’, with the loss of ON g between vowels marked by hiatus (cf. ON boga > SG bogha, q.v.) and with intervocalic k yielding SG g regularly.
McDonald (2009, 347) apparently concurs with this thesis, but later (2015a, 122–23) is uncertain.
Lockwood supposes (1963, 56) that budhaigir is of unknown provenance, although he earlier suggests (1961, 66–67) a correspondance between SG buigeir and Far. (Suðuroy) bukari ‘striker’, 
Based on the verb buka in the sense ‘to beat, strike, drub’. The Faroese bird name is found only in Nicolai Mohr’s dictionary MS (Den Nye Kongelige Samling 1287, fol. 64: ‘bugari vid. drunkvuidi’, fol. 84: ‘drunkvujti, s.m. “Søren Peder, Procellaria pelagica”’, but is cited in Svabo 1966, as Lockwood (1968, 102) notes. A form bugari would suggest a derivation from the verb buga ‘to bend, bow, curve’.
However, Far. buka ‘to strike etc.’ is related to Nn. boka ‘to soften by pounding, dig, root’ (Torp 1992, s.v. bŏka, with a long stressed vowel) and Scots bok (Shetland) [bok], [bōk], [bōək] ‘to squeeze, press down with small jerks, stamp, trample’ (Jakobsen 1928, s.v.). A Scots (Shetland) *boker 
With the agentive suffix -[ər], the equivalent of Far. -ari.
Lockwood (1984, 35–36) takes bulker to represent SG *bulgair, based on bulg in the sense ‘belly’, comparing the alternative name builgeun, which he takes to mean ‘belly-bird’ (< bulg + eun ‘bird’). However, builgeun may simply arise from bu(i)lg in the sense ‘bulge, blister’, with reference to the bird’s beak; cf. Scots coulterneb ‘coulter[-shaped] beak’.