Cadet
early 17th century (in cadet (sense 2)): from French, from Gascon dialect capdet, a diminutive based on Latin caput ‘head’. The notion ‘little head’ or ‘inferior head’ gave rise to that of ‘younger, junior’.
wiktionary
Borrowed from French cadet, from Gascon capdet, from Late Latin capitellum(“small head”). Attested in English from 1634. [1] [2]
Doublet of caddy, caudillo, and capitellum.
etymonline
cadet (n.)
c. 1610, "younger son or brother;" 1650s, "gentleman entering the military as a profession;" from French cadet "military student officer," noun use of adjective, "younger" (15c.), from Gascon capdet "captain, chief, youth of a noble family," from Medieval Latin capitellum, "little chief," literally "little head" (hence, "inferior head of a family"), diminutive of Latin caput "head" (from PIE root *kaput- "head").
"The eldest son being regarded as the first head of the family, the second son the cadet, or little head" [Kitchin]. Younger sons from noble families were sent to French court to serve as officers, without rising through the ranks or attending military school, after being attached to a corps without pay and enjoying certain privileges. This gave the word its military meaning "accepted candidate for a commission who is undergoing training to become an officer." Meaning "student at a military college" is from 1775.
Via the Scottish form cadee comes caddie "a messenger boy," especially one who carries clubs for a golfer, and slang cad.
