Real Dictionary

chaperon in American English
a person, esp. an older or married woman, who accompanies young unmarried people in public or is present at their parties, dances, etc. to supervise their behavior
to act as chaperon (to)
intransitive verb: to act as chaperon
noun: 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
transitive verb: to attend or accompany as chaperon

chaperon in British English
noun: (esp formerly) an older or married woman who accompanies or supervises a young unmarried woman on social occasions
verb: to act as a chaperon to