FromMiddle Frenchceste, fromOld Frenchceste, fromVulgar Latin*ecce ista, feminine of*ecce iste.
The loss of internal /s/ triggered compensatory lengthening of the preceding vowel. Due to the unstressed position of this pronoun, however, the length was soon lost again, which explains the spelling without a circumflex (though the formcête was occasionally used). Comparenotre andle nôtre.
cette f
cette