Found:

vowel harmony

PHONOLOGY: an assimilation process involving vowels of different syllables. EXAMPLE: in Turkish, the vowels of a suffix that are [+high] assimilate to the vowel of the stem with respect to the features [back] and [round]:

v	- evim	'my house'	göz	- gözüm	 'my eye'

gul	- gulum	'my rose'	basj	- basjïm 'my head'