ONlwSG

beòir f. [ˈb̥jɔːɾʲ], gen. beòire -[ə], beòrach [ˈb̥jɔːɾəx], ax], ɔx], ‘beer, ale’ is derived from ON bjór acc. m. ‘strong beer’, although commentators usually cite bjórr nom.; 

Craigie (1894, 164: SG beóir); Cameron (in MacBain 1894a, 619); Stewart (2004, 408); McDonald (2009, 342: SG beóir); Ó Muirithe (2010: SG beóir).

as is Ir. beoir 

Bugge (1912, 301: Ir. beor, beoir, beoil (after O’Clery [1643] and O’Reilly [1864]); Sommerfelt (1949, 233); McDonald (2009, 342: Ir. beor, beoir); and Ó Muirithe (2010: Ir. beóir).

and EG beóir; 

Stokes (1892, 126); Craigie (1894, 164); Meyer (1906, 201); and Marstrander (1915a, 79–80: ‘the loan is under no circumstances later than the 10th c.’); so also eDIL^˄; de Vries (1962); Schulze-Thulin (1996, 104); Kelly (2000, 335: biórr); McDonald (2009, 342); and Ó Muirithe (2010).

although MacBain (1896; 1911: beór) and MacLennan (1925: idem) cite both OEng. bēor and ON bjórr. A development of ON bjór acc. to SG beòir is regular, with alternation between final non-palatal and palatal lenited r in Gaelic, although beòir might represent a normalised dative form of an earlier *beòr.

The Scottish Gaelic word seems more or less restricted to literary usage today, although Faclan bhon t-Sluagh^˄ cites (Skye) beoir, beòthair ‘beer’, the usual word being leann m. (also lionn, liunn < EG linn nt. ‘drink, liquid’, more specifically ‘brew, ale, beer, intoxicating drink’ (eDIL^˄, s.v. ²linn)). While MacDomhnuill (1741, 24) distinguishes between béoir ‘beer’ and lionn ‘ale’, in Shaw (1780), Armstrong (1825) and HSS (1828) the terms seem more or less interchangeable.

Derivatives: beòir chaol f. (leann caol m.) ‘small beer’.