Why was "tantrum" trending last week?
1750, from French étiquette "prescribed behavior," from Old French estiquette "label, ticket" (see ticket).
The sense development in French perhaps is from small cards written or printed with instructions for how to behave properly at court (cf. Italian etichetta, Spanish etiqueta), and/or from behavior instructions written on a soldier's billet for lodgings (the main sense of the Old French word).
system of rules and conventions that regulate social and professional behaviour. In any social unit there are accepted rules of behaviour upheld and enforced by legal codes; there are also norms of behaviour mandated by custom and enforced by group pressure. An offender faces no formal trial or sentence for breach of etiquette; the penalty lies in the disapproval of other members of the group. Regardless of its level of material culture, any highly stratified society will possess an etiquette in which every person knows the behaviour expected from him toward others and from others toward himself.