kowtowyoudaoicibaDictYouDict[kowtow 词源字典]
kowtow: [19] The approved Chinese method of signifying respect for the emperor or other august personages was to prostrate oneself so that one’s forehead touched the ground. This was expressed in Mandarin Chinese by the term ke tóu (ke means ‘knock, bump’ and tóu ‘head’). English took the word over in the early 19th century and spelled it in various experimental ways (koo-too, ka-tou, kotow, etc) before settling on kowtow in the early 20th century.

The first writer on record as using the word in the metaphorical sense ‘defer servilely’ was Benjamin Disraeli in his Vivian Grey 1826: ‘The Marqess kotooed like a first-rate Mandarin, and vowed “that her will was his conduct”.’
[kowtow etymology, kowtow origin, 英语词源]
kowtow (n.)youdaoicibaDictYouDict
also kow-tow, 1804, from Chinese k'o-t'ou custom of touching the ground with the forehead to show respect or submission, literally "knock the head," from k'o "knock, bump" + t'ou "head." The verb in the figurative sense of "act in an obsequious manner" is from 1826. Related: Kowtowed; kowtowing.