Green’s Dictionary of Slang

rack v.2

[rack n.2 (3)]

1. [1940s–60s] (orig. US black) to go to sleep.

2. [1950s+] (US, also rack in) to sleep; thus racked out adj., asleep.

3. [1950s+] (also rack with) to seduce a woman, to make love.

In compounds

rack date (n.)

[1970s] a seducible female.

In phrases

rack out (v.)

[1960s+] (US) to fall asleep, to go to bed.