jam (2) — ODE

jam2 /dʒam

▸ noun [mass noun] a sweet food made from fruit and sugar boiled to a thick consistency, often eaten spread on bread:

strawberry jam

[as modifier] jam doughnuts.

▪ British English used in reference to something easy or pleasant:

they want it all, both ways and with jam on the top.

▸ verb

( jam2, jamming, jammed)

[with object] make (fruit) into jam.

– PHRASES

jam tomorrow British English
a pleasant thing which is often promised but rarely materializes:

a promise of jam tomorrow wasn't enough to satisfy them.

[phrase from Lewis Carroll's Through the Looking Glass (1871)]

put on jam (also lay on jam) Australian English informal
adopt an affected way of speaking or an affected manner:

when nervous, she tends to put on jam.

– ORIGIN mid 18th century: perhaps from jam1.