lay up v.
1. [mid-19C+] (also lay to) to rest, to relax.
2. [late 19C] (US) to die.
3. [1920s] to live, to be in a place.
4. [1920s+] (US, also lie up) to hide, to take refuge.
5. see lay back v.
[2000s] (US black) of a man, to penetrate a woman.