1984, "the linked computer networks of the U.S. Defense Department," shortened from internetwork, inter-network, which was used from 1972 in reference to (then-hypothetical) networks involving many separate computers. From inter- "between" + network (n.). Associated Press style guide decapitalized it from 2016.
1750, from French étiquette "prescribed behavior," from Old French estiquette "label, ticket" (see ticket (n.)).
The sense development in French perhaps is from small cards written or printed with instructions for how to behave properly at court (compare 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).
<a href="https://www.etymonline.com/word/netiquette">Etymology of netiquette by etymonline</a>
Harper, D. (n.d.). Etymology of netiquette. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/netiquette