The only free and comprehensive online etymological dictionary of the Spanish language
mucho (Adjective) "much"
10th cent. Old Spanish muito, later muncho, mucho, much. From Latin multus 'id.' From Proto-Italic *molto- 'id.' Perhaps from a late Proto-Indo-European root *mol-to- 'id.' or perhaps of unknown origin.
Asturian munchu, Portuguese muito, Galician moito, Catalan molt, French moult, Italian molto, Aromanian multu, Romanian mult