The rules of writing a thank you note are an example of etiquette.
Origin of etiquette
- French from Old French estiquet label ticket
From American Heritage Dictionary of the English Language, 5th Edition
- 1740, from French étiquette "property, a little piece of paper, or a mark or title, affixed to a bag or bundle, expressing its contents, a label, ticket" from Middle French estiquette (“ticket, memorandum”), from Old French estiquette, from estechier, estichier, estequier "to attach, stick", (compare Picard estiquier "to stick, pierce"), from Frankish *stikkan, stikjan (“to stick, pierce, sting”), from Proto-Germanic *stikaną, *stikōną, *staikijaną (“to be sharp, pierce, prick”), from Proto-Indo-European *st(e)ig-, *(s)teig- (“to be sharp, to stab”). Akin to Old High German stehhan "to stick, attach, nail" (German stechen "to stick"), Old English stician "to pierce, stab, be fastened". The French Court of Louis XIV at Versailles used étiquettes, "little cards", to remind courtiers to keep off of the grass and similar rules. More at stick (verb), stitch.