Green’s Dictionary of Slang

1. (also well-end) of a man, having notably large genitals.

[1890		C. Pearl in Blatchford Memoirs (1983) 125: He was a fine and intelligent man, who soon turned out to be [...] well-shaped and well-equipped].
1951		N. Montsarrat Cruel Sea 302: ‘I’m not rich.’ [...] ‘You are doubtless well-endowed [...] It’s better, really [...] A lot of women think so.’ .
1972		B. Rodgers Queens’ Vernacular 211: Having more than seven inches of cock [...] well endowed.
1974		Maclean’s (Toronto) July 25: Gradually I learned the swingers’ lingo: ‘TVs’ meant transvestites; ‘toys’ meant anything from vibrators to whips; [...] ‘uncut’ mean uncircumcised, and ‘well-end’ an abbreviation of ‘endowed.’.
1981		S. Berkoff Decadence in Decadence and Other Plays (1985) 30: You know I’m quite well endowed.
1993		K. Lette Foetal Attraction (1994) 29: Archibald, whose underpants size was bigger than his IQ. ‘And’, added Gillian, ‘we’re not talking well endowed.’.
2000		H. Dowd ‘Crazy Summer’ 🌐 From the way she described it, it would be considered well endowed by anyone’s standards, even that show-off Hammerhead.

2. of a woman, having notably large breasts.

1968		P. Barnes Ruling Class Prologue: Miss Shelley seems well-endowed, sir.
2000		F. Mac Anna Cartoon City 41: She had been so well endowed that Bob Casper had joked that she must be carrying her groceries down the front of her shirt.