13th cent. From Latin felicem, accusative of felix "happy," but earlier "fruitful."
From Proto-Italic *fēlwī-, which de Vaan (2014) evincingly interprets as "with young." From Proto-Indo-European *dheh1-lu̯-i- 'id.,' a hypercorrection of earlier *dheh1-lu̯- 'id.' From the noun *dheh1-l- "young animal." From the root *dheh1- "to suckle."
As there were myriad Catholic saints named Felix, myriad names and surnames appeared throughout Spain in Christian reverence: Feliz, Félez, Felices, Felies, Felis, San Félix, Félix, San Félix, Santelices, Sanfelis, and Sanfiz.
Asturian feliz, Portuguese feliz, Galician feliz, Catalan feliç, Italian felice, Romanian ferice
Middle Irish deil "sow"
Old High German tila "nipple," Old English delu 'id.'
Lithuanian dėlė̃ "leech," Latvian dēle 'id.'
Ancient Greek θῆλυς (thêlus) "female"
Armenian dayl "beestings"
Sanskrit dhārú- "suckling"