Charmer comes from charm + -er. Charm is from Old French charme ('magic spell, incantation'), from Latin carmen ('song, incantation, verse'), from canere ('to sing'). The historical trail runs through charme in Old French, carmen in Latin, and canere in Latin. Morphologically, charmer is transparent: it draws on charm + -er. Used as a noun, charmer now means "a person with an attractive, beguiling manner", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in related forms such as charm, charming, and enchant. The result is a borrowed or transmitted form whose modern spelling carries a compact record of its route into English.