Uncertain.[1] Phonetically impossible is any connection with Proto-Indo-European*bʰey- which gave instead fūcus(“drone”). Traditionally also hypothesized as from Proto-Indo-European*e/a(m)p-i-(“stinging insect; bee”), related to GermanImme(“bee; swarm of bees”), Old Englishimbe and Ancient Greekἐμπίς(empís, “a stinging or biting insect”). However, this has characteristics of a European substrate word. According to Vennemann's Atlantic substrate theory, the ultimate source may be a Semitic word cognate with Egyptianꜥfj(“bee”) (though no attested Semitic cognates survive); de Vaan finds this plausible. Another hypothesis suggests an Oscan-Umbrian loan from an original *akuis(“sharp, stinging”) (e.g. Latinaqui-(“sharp”) in aquifolius, aquilinus); the Osco-Umbrian reflex of Proto-Indo-European labiovelar */kʷ/ that gives Latin <qu> is regularly /p/.
De Vaan, Michiel (2008) “apis”, in Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill, →ISBN, page 47
“apis”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
“apis”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
apis in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
apis in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.
“apis”, in The Perseus Project (1999) Perseus Encyclopedia
“apis”, in Harry Thurston Peck, editor (1898), Harper's Dictionary of Classical Antiquities, New York: Harper & Brothers
“apis”, in William Smith, editor (1848), A Dictionary of Greek and Roman Biography and Mythology, London: John Murray
“apis”, in William Smith, editor (1854, 1857), A Dictionary of Greek and Roman Geography, volume 1 & 2, London: Walton and Maberly
