Green’s Dictionary of Slang

line n.1

SE in slang uses

In phrases

first line (n.) [SE first, best + line (of merchandise]

[1970s] (drugs) morphine.

go down the line (v.)

[1950s] to make an effort, to commit onself.

have a line on (v.) [racing jargon the line, the daily details of the horses running and the odds on them]

[20C+] to understand, to know what is happening; to know about.

in line (adj.)

[1940s+] not breaking any rules, law-abiding.

keep the line (v.) [hunting jargon keep one’s own line, to ride straight]

[early–mid-19C] to behave properly.

line of the old author (n.) (also leaf of the old author) [? the old author being God]

[late 17C–early 19C] a drink, esp. of brandy.

on the line

see separate entry.

out of line (adj.) [SE line, a style of activity, a discipline]

[1920s+] (orig. US) breaking rules, unacceptable, out of the ordinary.

over the line

1. [1920s] drunk.

2. [1910s] to excess.

under the line

[mid-19C] (UK Und.) awaiting execution by hanging.

In exclamations

hold the line! [telephone imagery]

[1920s–30s] wait a minute!