Green’s Dictionary of Slang

C-note n.

[C n.2 ]

1. (US) a $100 bill.

[US]C. Panzram Journal of Murder in Gaddis & Long (2002) 171: Some skunk [...] can be hired for a C note or less to bump him off.
[US]R. Chandler ‘Pearls Are a Nuisance’ in Spanish Blood (1946) 109: ‘Put a C-note on the table.’ I took my wallet out and extracted from it one of the two hundred-dollar bills.
[US]W. Brandon ‘Its so Peaceful in the Country’ in Ruhm Hard-Boiled Detective (1977) 323: She asks me, will I really come back, and I tell her I cross my heart for a C note I will come back on the hour.
[US]N. Algren Walk on the Wild Side 144: Sure enough, folded neatly quartered, so as to let him read the ‘100’ without unfolding it, Finnerty’s c-note still waited to be spent.
[US]T. Thackrey Gambling Secrets of Nick The Greek 243: The hustler laughed and refused Nick’s extra C-note.
[US]‘Iceberg Slim’ Airtight Willie and Me 18: He saw Willie let fall and retrieve our lone ‘C’ note.
[US]J. Ellroy Brown’s Requiem 23: There must have been sixty or seventy C-notes.
[US]J. Ellroy ‘Gravy Train’ in Pronzini & Adrian Hard-Boiled (1995) 490: They walked out thumbing C-notes.
[US]L. Stringer Grand Central Winter (1999) 124: Richard [...] triumphantly returns, clutching a check for seven grand, and hits me off with a C-note.
[US]C. Goffard Snitch Jacket 172: Spot me a C-note?
[US]S.M. Jones Lives Laid Away [ebook] ‘When was the last time you heard of some government grunt whippin’ out a C-note for anything?’.

2. (US prison) a 100-year jail sentence.

[US]C. Shafer ‘Catheads [...] and Cho-Cho Sticks’ in Abernethy Bounty of Texas (1990) 201: C- note, n. – a hundred-year sentence.

3. (US black) a one-year sentence.

[US]T.R. Houser Central Sl. 15: C-note A jail sentence of one year.