Green’s Dictionary of Slang

gas n.2

[gas v.2 ]

[1940s+] (US black) hair that has been artificially straightened or ‘processed’.

In compounds

gashead (n.) [1960s+] (US black)

1. one who has had their hair straightened with a ‘process’ haircut.

2. in fig. use, a black person who rejects their racial origins.