also kow-tow, 1804, from Chinese k'o-t'ou custom of touching the ground with the forehead while kneeling as a gesture of respect or submission, literally "knock the head," from k'o "knock, bump" + t'ou "head."
also kow-tow, 1826 in the figurative sense of "act in an obsequious manner," from kowtow (n.). Literal sense in English is from 1848. Related: Kowtowed; kowtowing.
He is always kowtowing to his boss