Green’s Dictionary of Slang

1. (US Und.) a betrayal, a confession.

1915		S. Ford Torchy, Private Sec. 112: ‘What did you use on our young friend, persuasion, or assault with intent?’ ‘On a fish-face like that? [...] This was just a simple case of spill.’.
1942		C. Himes ‘Strictly Business’ in Coll. Stories (1990) 141: When he got the word that the spill was on the turn, he went green as a summer salad.
1958		E. Aarons Gang Rumble (2021) 13: [S]omebody said there was a spill. Somebody said the Violets know.
2007		S. Maloney Sucked In 56: I hear there’s a spill in the offing.

2. (US black) publicity, promotion.

1935

Ted Yates This Is New York 26 Apr. [synd. col.] He’s getting his first real column spill here.