The word cloak was borrowed into English around the turn of the thirteenth century with the spelling cloke. Throughout Middle English, it also took the forms of clooke, clocke, cloik, clok, cloak, and cloake until cloak was standardized in the 1700s. It comes from the Old North French word cloque, which still meant "cloak", and that's from Medieval Latin clocca, or "bell". The connection was that cloaks back then were thought to have bell-like shapes (this also makes it a relative of the word clock). Beyond that, the etymology is unknown, but it's thought that it could ultimately be a Celtic word spread by Irish missionaries, and it would ultimately be onomatopoeic in origin. The phrase cloak and dagger is an 1848 calque of a French phrase and the verb to cloak emerged from the noun in the early sixteenth century.
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.