Clauson (1972)
An etimological dictionary of pre-thirteenth-century Turkish
p. 866
F şad
Iranian l.-w. in a form not found in any known dialect, but cognate to Saka sao, Sogdian ’ysyδ, Pe. şah, ultimately der. fr. Old Pe. xšāyaθiya. In Turkish the title, ranking prob. next after xağan and bestowed by the xağan on some close relative, younger brother or son, often carried with it the duty of ruling part of the xağan’s dominions, so that ‘viceroy’ is perhaps the nearest English equivalent, but not an exact translation. In Turkish, apart fr. one occurrence in Uyğ. and a very dubious one in O. Kır., Alai. 2, 1, pec. to Türkü, but various Turkish şads are mentioned in the Chinese records, the word being transcribed sha, she, or ch’a, see Chavannes, Documents sur les Tou-kiue (Turcs) occidentaux, St. Petersburg, 1900, p. 320. Cf. yabğu:. Türkü viii tört yegirmi: yaşımka: Tarduş bodun üze şad ertim (II olurtım) ‘in my 14th year I was (assumed the post of) şad over the Tarduş people’ I E 17, II E 15; (with my younger brother Kül Tegin and) eki: şad birle: ‘the two şads’ I E 27 (II E 22); (the Türgeş xağan and his army attacked) xağanı:n yabğu:sı:n şadım anta: ölü:rtim ‘I killed their xağan, yabğu:, and şad there’ II E 28; uluğı: şad erti: ‘their (the 700 men’s) headman was a şad’ T 5; şad atığ anta: bermiş ‘he gave him the title of şad there’ Ongin 6; o.o. I N 11; I E 14, II E 12; T 31, 41, etc.: Uyğ. viii eki: oğluna: yabğu: şad at bertim ‘I gave my two sons the title of yabğu: and şad respectively’ Şu. E 7.