I'm not sure how it came about, but the term also came to be used for making a woman pregnant. My mind boggles about how the term came to have this other meaning and I did wonder that, if the "knocker up" 'knocked' too early, the double entendre, "early rise", could have resulted in the impregnation in those days preceding birth control.
|A ?Knocked Up Lady 'Knocker Up' Takes Aim at an Upper Window
Back in 1960 near the Beardmore Glacier in Antarctica I became stranded at a primitive weather station with a few Americans manning the outpost. One night I left the comfort of their Nissen hut for my polar tent and asked a RNZAF person there to 'knock me up ' at six the next morning because I had a radio call the next morning. The following morning I was interrogated by the Americans who only knew of the impregnation definition of the phrase. They were a bit sceptical of my explanation of the term!
|Crew at Beardmore Depot
In the photo above, from left, Peter Rule(one of the rescued RNZAF airmen), 'Carp' USA (whose father was killed in the WW2 attack on Pearl Harbour), Athol Boag (RNZAF who was asked to 'knock me up), two from USA, 'Con' who had the interest in the differences between American and English phrases.
There is a very interesting discussion of the phrase in the linked discussion here. And the interesting story of the RNZAF rescue is recorded here and here. It also is in one of my previous blogs - and presently featured above - about the antarctic rescue.