cog

Cog is a Scandinavian loan that arrived in English with the Norse settlement of northern and eastern England.‍​‌​‍​‌​‌​‌​‍​‌​‌​‌​‌​‌​‌​‍​‍​‍​‍​‌​‍​‍​‌​‌​‌​‌​‌​‌​‌​‍​‌​‌​‍​‍ Old Norse 'kugg,' still preserved in Swedish 'kugg' and Norwegian 'kug,' meant a tooth or projection set into the rim of a wheel — the kind of wooden peg that meshed with another wheel in a watermill or windmill. Middle English 'cogge' is recorded from the 13th century, and the word has stayed close to that meaning. The figurative 'cog in the machine,' meaning a small but essential and interchangeable part of a larger system, is an 18th-century coinage that capitalised on the long industrial-era dominance of geared machinery. A separate Middle English 'cog' meaning a type of broad medieval ship is unrelated, from a different Germanic root.