1683: knock up Jul 24, 2019

Although the phrase 'knock up' has been used since the 17th century to mean 'knock on a door', this is not related to the other meaning of 'get pregnant', which originated in American in the 19th century. It's not to say that the words themselves are different, but that 'knock' already had a connotation to copulation (think 'knocking boots') such as in 'knock-shop' meaning 'brothel'. In fact, that phrase is much older than the more literal meaning 'knock up'. In this way, the phrase has gained meanings in cycles. For more about etymologies, and how to discern things for yourselves, see the latest video: https://youtu.be/AviuxNIvdPM