ONlwSG

càl m. [kʰɑːɫ̪], gen. càil [kʰaːl], in the sense ‘cabbage’ is derived by Cox (1991, 492) from ON kál nt. ‘cabbage, and all sorts of large-leaved plants’ (NO); Cox is followed by McDonald (2009, 370).

Stewart (2004, 408) also derives SG càl from ON kál, ostensibly after MacLennan (1925), although MacLennan simply lists ‘Scots kail. OEng. cawl. Lat. caulis. ON kál’, apparently without differentiation.

While ON kál would indeed be expected to yield SG [kʰɑːɫ̪], MacBain (1911) derives SG càl, along with Ir. cál, W cawl, C caul (kowl) and Bret. kaol, from Lat. caulis ‘stalk’, ‘whence likewise Eng. cole and Scots kail’. However, as Lat. Paulus gives Ir. Pól and SG Pòl (and SG Pàl, either via o ~ a alternation, or from Scots Paul [ˈpɑːl], [ˈpɔːl], Northern Ireland [ˈpaːl] (The Online Scots Dictionary^˄)), Lat. caulis might be expected to yield Ir. *cól, SG *còl.

A number of other words for ‘brassicas or cabbage-type plants’ appear to have been borrowed into Scottish Gaelic and Irish over time, presumably for different reasons or under different circumstances, e.g. SG praiseach ‘cabbage’ (Dwelly 1911, after Cameron 1900), Ir. praiseach ‘pottage; (wild) cabbage, kail’ (Ó Dónaill 1977) (< Lat. brassica (eDIL^˄, s.v. praisech)); 

Although the ending has been adapted, falling together with the native suffix -ach.

SG cabaiste ‘cabbage’ (Dwelly), Ir. cabáiste ‘idem’ (Ó Dónaill) (< Eng. cabbage); SG còlais ‘cabbage’ (Dwelly, after Armstrong 1825), early modern Ir. cóilis ‘idem’ (eDIL^˄) (< Lat. caulis); and early modern Ir. caḃlán, coḃlán ‘kale, cabbage’, diminutive of caḃal ‘cabbage colewort’ (eDIL^˄) (< OEng. cāwel).

MEng. cōl(e) and the northern equivalent cāl, kāl (now kale, kail) point back either to OEng. cāl (contracted from cāwel, cāwl), or to ON kál, both from Lat. caulis (OED^˄), and Ir. cál probably derives from OEng. cāl. SG càl probably also derives from OEng. cāl, or rather Pre-Literary Scots *cāl, 

Hence Scots kail /kel/, northern MEng. ā yielding EScots /a:/ > MScots /e:/, shortening to /e/ from the mid-15th century onwards (Aitken 2002, 114).

although we can probably not exclude the possibility that ON kál was also borrowed into Early Gaelic.