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v1.0: 01/10/24
biorsamaid f. [ˈb̥juʂəmad̪̥ʲ], [ˈb̥irsəmad̪̥ʲ], 
(Invergarry, North Laggan) [bjwʴsəmɑdʹ] (≈Faclan bhon t-Sluagh˄: ‘the turned ʴ is used for the symbol which is unclear in the original’); (Ness in Lewis) [piɯ̯ʂɣəmatj], [piʂɣəmatj] (Morrison 2020, 162, 179); (Ness in Lewis, Achlyness in West Sutherland, Invergarry) /biRsəmadʲ/ (AFB˄).
Bugge (1912, 300) and Henderson (ibid.) derive this word from ON bismari m. ‘steelyard balance’; so also de Vries (1962), Stewart (2004, 408) and McDonald (2009, 342). On the other hand, MacBain (1911, 38) derives the word from Scots bismar (also bismer, bismore, bysmer [′bɪsmər] and (Orkney) pismire 
Cf. Martin 1703, 361: pismore.
Note that Wilson (1984, 74) includes biorsamaid in his Appendix 2: Norse Loan-words in Irish – Commerce, citing Bugge (1912, 300), but the latter is himself citing MacLeod and Dewar (1839), a Scottish Gaelic dictionary.
Although it has also been recorded in Uist (McDonald 1972), West Sutherland and the Invergarry area (e.g. Faclan bhon t-Sluagh˄, see above).
SG stailleart m., also stallart, ‘steelyard balance’ is a loan from Scots stalliard.
≈MacAskill notes that ‘cothrom is often used in Lewis and sometimes in Harris for “scales, balance”. Meidh is also used in Harris, as is tomhais, the usual word in Barra and Uist, and in some areas of Lewis. In Skye the form is tomhaisean, shortened in South Uist to toisean. For “spring-balance” the usual word in most areas of Lewis is biorsamaid, but elsewhere stailleart is used, as in the other islands.’ MacLeod (1999, 101) gives both ‘biorsamaid’ and ‘stailleart’ for steelyard; Shaw (1780) gives ‘meigh thomhais’ (sic) for steelyard.
‘Steelyard balance (Roman balance)’ (e.g. HSS (1828), McAlpine (1832), MacLeod and Dewar (1839), Dwelly (1911), AFB˄. Dwelly also gives the sense ‘term of contempt, applied to a sharp-tongued woman’, ?cf. Scots bismere ‘disreputable woman’ (DOST˄).
‘Spring balance (Newton meter)’ (e.g. Henderson (1910, 133), MacAskill (1966, 78), Faclan bhon t-Sluagh˄, MacLeod (1999, 101) and Morrison (2020, 162, 179).
While ON bismari and Scots bismar would formally yield SG *[ˈb̥is̪məɾʲə] and *[ˈb̥is̪məɾʲ], respectively, it seems more likely that SG biorsmaid is a loan-blend from Scots bismar, 
Although Jamieson (1808) also notes the Scots form bissimar.
Cf. SG Mosgail for Morsgail and mu(i)sgian for muirsgian (Cox 2022, 821–22).
Note that HSS (≈1828) records the folk etymology bior sa mhaide, with bior m. ‘small pointed object’, sa ‘in the’ and (len.) mhaide m. ‘stick or rod’.