Green’s Dictionary of Slang

syrup n.

1. alcohol; a drink.

[UK]A. Binstead Pitcher in Paradise 146: Finally he gets a bit leg-weary, an’ none the better for all the syrup he’d had.

2. (US) money.

[US]A. Baer Two and Three 24 Feb. [synd. col.] The old gravy is just going to be oozing off baseball receipts, boxing is going to be smothered in syrip, and there will be four layers of the old sugar on [...] college athletics.

3. (US) nitroglycerin, as used as an explosive.

[US]O. Von Gulker ‘Boomtown Album’ in Botkin Folk-Say 229: A sharpshooter hauls the nitro soup around and handles the blowing of holes. Buddy [...] might be seen any time racing up and down the low-lying Osage foothills delivering its dangerous ‘syrup’ to wells.

4. (US drugs) a codeine-based prescription cough syrup.

[US]UGK ‘P.A. Nigga’ 🎵 I’m a big body flipper, syrup sipper.
The Ampersand 6 Feb. 🌐 It’s about purple stuff/syrup/purple drank/lean, a popular recreational drug concoction which combines cough syrup and (usually) Sprite.
I Kirkman ‘Cocaine Starlight’ in ThugLit Nov.-Dec. [ebook] [H]er eyes are codeine-coated nebulas. She's fucking with the syrup again.