[...]MacBain's Etymological Dictionary of Scottish Gaelic [5] has: siabhrach = a fairy, sìobhrag (Arran), siobhrag (Shaw), sìbhreach (M`A.), Irish siabhra, Early Irish siabrae, siabur, fairy, ghost, Welsh hwyfar in Gwenhwyfar, Guinevere (?): *seibro-: sìochair = a dwarf, fairy, Middle Irish sidhcaire, fairy host, síthcuiraibh (dat.pl.), Early Irish síthchaire; from síth, fairy, and cuire, host (German heer, army, English herald). sìth.1 = a fairy, sìthich (do.), Irish sídh, a fairy hill, sígh, a fairy, sígheóg (do.), Old Irish síde, dei terreni, whose dwelling is called síd; in fact, síde, the fairy powers, is the pl. (ge. s. ?) of síd, fairy dwelling or mound, while its gen. sing. appears in mná síde, fir síde: *sêdos, g. sêdesos, as in the case of sìth, peace, which is its homonym (Stokes); root se, sêd, Greek @Ge@`dos, a temple or statue, literally an "abode" or "seat"; Latin noven-sides, noven-siles, the new gods imported to Rome. Thurneysen has compared Latin sîdus, a constellation, "dwelling of the gods". Hence sìthean, a green knoll, fairy knoll.