Clauson (1972)
An etimological dictionary of pre-thirteenth-century Turkish
p. 886
yétti:
(yéddi:) ‘seven’. There is no doubt that the medial consonant was originally double, cf. ékki:, q.v. C.i.a.p.a.l. The original voiced consonant survives in the Kıp. forms listed below and in SW Az. yeddi; Osm., Tkm. yedi; and the double consonant in SE Türki yette BŞ 648, yetti Jarring 135: SC Uzb., NW Kumyk yetti: SW Az. yeddi. For the -é- cf. yétmiş. Türkü viii over a dozen occurrences, yéti: commoner than yeti:: viii ff. Man. yéti is common: Yen. yéti: yegermi: ‘seventeen’ Mal. 26, 5; yéti: do. 48, 9: Uyğ. ix inim yéti: ‘I had seven younger brothers’ Suci 6: viii ff. Man.-A, Man., Bud., Civ. yéti is common: Xak. xi (by itself, under the heading fa‘lal, requiring four letters) yéti: (?read yétti:) ‘the number seven’; hence one says yéti: kat kö:k sab‘a aṭbāq mina’l-samāwāt ‘the seven layers of the heavens’ Kaş. III 27; yéti: III 227 (böke:): xiii(?) Tef. yéti: (once yetdü:) 152: xiv Muh. sab‘a ye:di: Mel. 81, 8; yéti: Rif. 186: Çağ. xv ff. yetti ‘the number seven’, also pronounced ba-taxfīf-i tā, i.e. as yeti San. 348v. 17 (on the -tt- see 20v. 9ff.): Xwar. xiv yéti Qutb 78: Kom. xiv ‘seven; a week’ yéti/yetti CCG; Gr.: Kıp. xiii sab‘a yéti: Hou. 22, 6: xiv yétti: (sic) al-sab‘a, originally (wa’l-aṣl) yedi:, also so pronounced İd. 91; sab‘a yeddi: (sic) Bul. 12, 11: xv yedi: Kav. 65, 7; Tuh. 60b. 7 a.o.o. (the forms w. -d- are prob. Tkm.): Osm. xiv and xv yedi occurs in several texts TTS III 810; IV 884.