Most people know that the disco genre of music was called that because it was played in discotheques, but there's so much more to it than all that. Discotheque comes from French, where it also meant "nightclub". This was modeled after the pre-existing term bibliotheque, meaning "library", but with the word disque ("disk") replacing the prefix. So a discotheque is a "record library". Makes sense. Disque comes from Latin discus, from Ancient Greek diskos, with the same definition. This derives from the verb dikein, meaning "to throw" (so diskos was adopted metonymically). This is reconstructed to Proto-Indo-European deykti, "to show". Meanwhile, bibiotheque, from whence the back-formation -theque came, was bibliotheca in Latin and bibliotheke in Ancient Greek, where it literally meant "book room". Here we can break it up into biblion, meaning "book" (with Attic origins), and theke, meaning "chest" (from tithemi, "to place", which comes from PIE deh, "to put"). So, if we go as far back as possible, disco means "to show putting books".
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.