Clauson (1972)
An etimological dictionary of pre-thirteenth-century Turkish
p. 973
yas-
basically ‘to loosen’, with some connotation of allowing something under tension to become flat; in its extended meanings more or less syn. w. 1 yaz- and, to some extent ya:d-, and therefore difficult to identify in some modern languages; but certainly survives in SE Türki yasi-: SW Osm. yas- and perhaps, NC Kır. jas-. Xak. xi beg sü:sin yasdı: ‘the beg disbanded (farraqa) his troops (and sent them) to their homes’; the origin is the phr. er ya:sın yasdı: ‘the man unstrung (nazala . . . al-watar ‘an) his bow’; and one says xa:n çowa:ç yasdı: ‘the xa:n loosened the fastening (ḥalla . . . ‘uqda) of the royal parasol which was raised over his head’ Kaş. III 59 (yasa:r, yasma:k): Kıp. xiii fakka min fakki’l-qaws min watarihi ‘to unstring (a bow)’ yas- Hou. 43, 1: xiv yaş- ditto İd. 94: Osm. xiv ff. yas- ‘to unstring (a bow)’, and (xvi ff.) ‘to flatten’; common TTS I 792; II 1009; III 777; IV 852: xviii (‘Rūmi’) San. 331v. 14.