E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Etiquette (3 syl.).
The usages of polite society. The word means a ticket or card, and refers to the ancient custom of delivering a card of directions and regulations to be observed by all those who attended court. The original use was a soldiers billet. (French, etiquette; Spanish, etiqueta, a book of court ceremonies.)
Etiquette had its original application to those ceremonial and formal observances practised at Court . The term came afterwards to signify certain formal methods used in the transactions between Sovereign States.Burke: Works, vol. viii. p. 329.