1910-15, Americanism; < Italian (Neapolitan dial.) guappo swaggerer < Spanishguapo pimp, ruffian, via dialectal French < Latinvappa wine that has gone flat, worthless person; initial w perhaps by association with a related Gmc word
derogatory for "Italian," 1912, Amer.Eng. slang, apparently from southern It. dialect guappo "dandy, dude, stud," a greeting among male Neapolitans, said to be from Sp. guapo "bold, dandy," which is from L. vappa "sour wine," also "worthless fellow;" related to vapidus (see vapid).