The only free and comprehensive online etymological dictionary of the Spanish language
pagar (Verb) "to pay"
12th cent. From Latin pacare, defined in Roberts (2014) as "to pacify (after having conquered)." A verb formed from pax "peace" (see paz).
Indo-European
Romance
Asturian pagar, Portuguese pagar, Galician pagar, Catalan pagar, French payer, Italian pacare, Romanian împăca, Sardinian pacare
Basque
Old Low Navarrese bakatu "pay," Roncalese pakatu 'id.,' both borrowed from Latin pacare; Bizkaian pagau "pay," borrowed from pagar