The only free and comprehensive online etymological dictionary of the Spanish language
ni (Adverb) "neither;" "not even," "even"
From Latin nec "not," an apocopated form of neque "and not," from ne "not" and -que "and." See no and -que respectively for further etymology.
Indo-European
Romance
Asturian nin, Portuguese nem, Galician nin, Catalan ni, French ni, Italian