The only free and comprehensive online etymological dictionary of the Spanish language
caer (Verb) "to fall"
10th cent. From Latin cadere 'id.' From Proto-Italic *kad-e/o- 'id.' From Proto-Indo-European *ḱh2d- 'id.'
Asturian cayer, Portuguese cair, Galician caer, Catalan caure, French choir, Italian cadere, Aromanian cad, Romanian cădea
Ancient Greek κεκαδών (?) (kekadón) "robbing"
Sanskrit śad- "to fall"

Following the Dictionnaire Étymologique Roman, there were two ways that Latin cadere was syllabified in Proto-Romance, which arose from disagreement over accentuation on the penultimate or the primary syllable. The first, Proto-Romance */ˈkad‑e‑re/, shows an accented first syllable *kad-, and is reflected in Catalan and a number of languages like Istriot cài. The second, Proto-Romance */kaˈd‑e‑re/, shows an accented penult *-de-, and is reflected in Spanish and the other Romance cognates listed above.