LSJ s.v. II notes that kh/lwn is used to mean "he-ass" in Archilochus fr.43 West. By extension, given the association of donkeys with priapism, it is used to refer to Pan by Cratinus fr.321 Kock, now 359 K.-A. The extension is recorded in lexicography as early as Aristophanes of Byzantium, Nomina aetatum (fragmentum Parisinum) 19: "kh/lwn is one prone to sex, as a metaphor from rutting donkeys". The gloss "hot for coitus" is Philoxenus fr.514, and is repeated in the Etymologicum Gudianum, the Etymologicum Magnum, and codices of the Lexicon of Cyril.
cf. generally kappa 1517.