Green’s Dictionary of Slang

1. (Aus., also jampot collar) a notably tall collar, up 4” high [resemblance].

1889-90		D. Sladen in Barrère & Leland Sl., Jargon and Cant I 493/2: ‘Me a Jute! why, what makes you ask that, Mary?’‘The collar. No one but Jews wears them jampots now.’.
1914		E. Pugh Cockney At Home 201: ‘Ah, an’ what price Alhambras an’ all?’ demanded a youth in a jam-pot collar.
1944		J. Cary Horse’s Mouth (1948) 33: Photographs of Mr Monday in a jampot collar.
1955		N. Pulliam I Travelled a Lonely Land (1957) 234/2: jam pot – a high, stiff collar worn by a city dude.

2. the vagina [jam n.³ (3)].

1890–1904		Farmer & Henley Sl. and Its Analogues.
1896		Farmer Vocabula Amatoria (1966) 45: Bouteille, m. The female pudendum; ‘the jam-pot’.
1966		Trimble 5000 Adult Sex Words and Phrases.
1982		Maledicta VI:1+2 (Summer/Winter) 131: Vagina […] jampot, jaxy, jelly roll […], jing-jang, joxy.

3. (US black/gay) the anus [jam n.² (4a)].

1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1965		Guild Dict. Homosexual Terms 25: jam pot (n.): The anus.
1972		B. Rodgers Queens’ Vernacular 19: the rectal opening, anus [...] jam-pot (particularly when licked by a rim-queen).