Kowtow
Kowtow, from the Chinese term kou tou (叩頭), is the act of deep respect shown by kneeling and bowing so low as to touch the head to the ground. While the phrase ke tou (磕頭) is often used in lieu of the former in modern Chinese, the meaning is somewhat altered: kou originally meant "knock with reverence", whereas ke has the general meaning of "touch upon (a surface)".
In imperial Chinese protocol, the kowtow was performed before the emperor. Current Chinese etiquette does not contain any situations in which the kowtow is regularly performed in front of a living human being, although it may occur in rare and extreme cases where one is begging for forgiveness or offering an extreme apology. The kowtow is often performed in groups of three before Buddhist statues and images or tombs of the dead. A sequence of three sets of kowtow was an extreme gesture of respect. The person would stand up and kneel down again between each set, hence the term three kneelings and nine kowtows (三跪九叩).
Kowtow came into English in the early 19th century to describe the bow itself, but its meaning soon shifted to describe any slavish support or grovelling.
Kowtow was very important in the diplomacy of China with European powers, since it was required to come into the presence of the Emperor, but it meant submission before him. Dutch traders had no problem to kowtow since they represented themselves, but the British embassies of George Macartney, 1st Earl Macartney (1793) and William Pitt Amherst, 1st Earl Amherst (1816) were foiled since kowtowing would mean acknowledging the King as a subject of the Emperor.
See also
de:Kotau