What's the meaning of the phrase 'Well endowed'?
A euphemism referring to large sex organs, in men or women.
What's the origin of the phrase 'Well endowed'?
'Well endowed, in the sense of 'having a plentiful supply of something' has been a recognised phrase in the language from almost the time before there was a language. There are examples of it in print in Middle English, for example, this extract from Sir John Fortescue's The Governance of England, circa 1475:
It shalnot only be goode to owre prince, but also to vs selff, that he be well indowed.
There are many examples in print of 'well endowed schools' and the like, from the Middle Ages onward. The 'having a plentiful supply of sex organs' meaning didn't emerge until the mid 20th century. Here's an early example of it in print, from W. Sheldon and S. Stevens's psychology textbook The Varieties Temperament, 1942:
Boris was sexually well endowed, in the sense that he had large genitalia, and poorly endowed in the sense that his body was relatively insensitive.
It may be that the above authors were using 'well endowed' in the earlier sense and just happened to be writing about sex organs. We can in any case date the slang usage to a date not much later, in Nicholas Monsarrat's novel The Cruel Sea, 1951:
‘I'm not rich.’... ‘You are doubtless well-endowed... It's better, really... A lot of women think so.’
The above applies to men with large penises, but women, by virtue of having large breasts, may be well endowed too. This usage emerged at much the same time as the male version. Here's an example from July 1951 from the US newspaper The Daily Sun:
Most women aren't as well endowed as Liz [Taylor]. How should they go about buying a suit?
Of course, with regard to the male 'well endowed' there is the equivalent phrase 'well hung'. This is most commonly thought of as an American expression and it is certainly more used there than in other places. It is in fact British in origin and dates from the 17th century. I wouldn't imagine that the Pilgrim Fathers took it with them across the Atlantic, but it's clear that someone did.