KNOCK HEADS

Right now, the word kowtow has essentially one usage: it's a political insult meaning "to act subserviently", normally to a group of people. But where did this word come from? Turns out it was a Chinese diplomatic act! In order to show fealty to the emperor, one would bow so low his head would touch the ground. Thus, kowtow meant "knock head" in Mandarin.  This is a portmanteau, of the words k'o ("knock") and t'ou ("head"). Since Chinese is weird compared to our Indo-European languages, t'ou is a phono-semantic compound, an etymological concept not present in our tongues and a tricky topic for transliteration. This means that an unrelated sound, tau, denoting plants, and the character meaning "head" combined to give us the word, and going further would be irrelevant (and besides, I'm hardly skilled enough to explain it more). Both of these terms are obviously of Sino-Tibetan origin, and kowtow has been steadily growing in popularity since its introduction in the mid-nineteenth century, especially in New Zealand, for some reason.