Chaperon

a person, usually a married or older woman, who, for propriety, accompanies a young unmarried woman in public or who attends a party of young unmarried men and women.
any adult present in order to maintain order or propriety at an activity of young people, as at a school dance.
a round headdress of stuffed cloth with wide cloth streamers that fall from the crown or are draped around it, worn in the 15th century.
to attend or accompany as chaperon.
to act as chaperon.
noun
(esp formerly) an older or married woman who accompanies or supervises a young unmarried woman on social occasions
someone who accompanies and supervises a group, esp of young people, usually when in public places
verb
to act as a chaperon to
n.

1720, “woman accompanying a younger, unmarried lady in public,” from French chaperon “protector,” especially “female companion to a young woman,” earlier “head covering, hood” (c.1400), from Old French chaperon “hood, cowl” (12c.), diminutive of chape “cape” (see cap (n.)). “… English writers often erroneously spell it chaperone, app. under the supposition that it requires a fem. termination” [OED]. The notion is of “covering” the socially vulnerable one.

“May I ask what is a chaperon?”
“A married lady; without whom no unmarried one can be seen in public. If the damsel be five and forty, she cannot appear without the matron; and if the matron be fifteen, it will do.”
[Catharine Hutton, “The Welsh Mountaineer,” London, 1817]

The word had been used in Middle English in the literal sense “hooded cloak.”

v.

“act as a chaperon,” 1792, also chaperone, from chaperon (n.), or from French chaperonner, from chaperon (n.). Related: Chaperoned; chaperoning.