Per Derksen, the root vowel stems from lengthening of the zero grade of Proto-Indo-European*gʰubʰ- from the root *gʰewbʰ-, with the addition of the Proto-Slavic suffix *-nǫti; the acute tone of the root is a secondary development, common in verbs ending in *-nǫti. Compare *gubìti(“to destroy”), the corresponding causative. Also cognate with *gъbnǫti(“to bend”). Other scholars reconstruct the PIE root differently from Derksen; see discussion under *gъbnǫti.
Chernykh, P. Ja. (1993) “ги́бнуть”, in Историко-этимологический словарь русского языка [Historical-Etymological Dictionary of the Russian Language] (in Russian), 3rd edition, volume 1 (а – пантомима), Moscow: Russian Lang., →ISBN, page 186
Vasmer, Max (1964–1973) “ги́бнуть”, in Oleg Trubachyov, transl., Этимологический словарь русского языка [Etymological Dictionary of the Russian Language] (in Russian), Moscow: Progress
Trubachyov, Oleg, editor (1980), “*gybnǫti”, in Этимологический словарь славянских языков [Etymological dictionary of Slavic languages] (in Russian), numbers 7 (*golvačь – *gyžati), Moscow: Nauka, page 218
References
^ * Derksen, Rick (2008) “*gỳnǫti”, in Etymological Dictionary of the Slavic Inherited Lexicon (Leiden Indo-European Etymological Dictionary Series; 4), Leiden, Boston: Brill, →ISBN, page 200: “v. (a) ‘perish’”
^ Olander, Thomas (2001) “gybnǫti: gybnǫ gybnetь”, in Common Slavic Accentological Word List[1], Copenhagen: Editiones Olander: “a (SA 211, 259; PR 133; MP 22)”