Green’s Dictionary of Slang

1. money.

1935		A.J. Pollock Und. Speaks.
1945		H.B. Darrach Jr. ‘Sticktown Nocturne’ in Baltimore Sun (MD) 12 Aug. A-1/1: A barnacle is a derelict of the old fleet; it is a point of honor among seamen who have any ‘line’ never to refuse a barnacle a belt.
1963		A.S. Fleischman Venetian Blonde (2006) 141: Now I was short of lines [...] he’d help me.
1969		‘Iceberg Slim’ Pimp 188: What kinda lines you got?
1971		(con. 1930s–50s) D. Wells Night People 118: Line. Money. When borrowing, ‘line’ doubles the amount actually required. Thus, ‘line fifty soft’ indicates a need for twenty-five cents and ‘line fifty hard’ for twenty-five dollars.

2. the cost or price of an item.

1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 257: line (n.): cost, price, money. Ex., ‘What is the line on this drape’ (how much does this suit cost)? ‘Have you got the line in the mouse’ (do you have the cash in your pocket)? (Also, in replying, all figures are doubled. Ex., ‘This drape is line forty’ (this suit costs twenty dollars).
1946		Mezzrow & Wolfe Really the Blues 218: Hold it down, Jim, and I’ll come up with line two like I said.

3. (Scot.) a bet.

2020

A. Parks Bobby March Will Live Forever 30: [T]he bookie’s boy, who came in to collect the lines from the regulars.