Cad
late 18th century (denoting a passenger picked up by the driver of a horse-drawn coach for personal profit): abbreviation of caddie or cadet.
wiktionary
Short for caddie, from Scots, from French cadet, from dialectal capdet(“chief, captain”), from Latin capitellum, diminutive of caput(“head”).
etymonline
cad (n.)
1730, shortening of cadet (q.v.); originally used of servants, then (1831) of town boys by students at Oxford and English public schools (though at Cambridge it meant "snob"), then "townsman" generally. Compare caddie. Meaning "person lacking in finer feelings" is from 1838.
A cad used to be a jumped-up member of the lower classes who was guilty of behaving as if he didn't know that his lowly origin made him unfit for having sexual relationships with well-bred women. [Anthony West, "H.G. Wells: Aspects of a Life," 1984]
