1. [mid-19C+] (also gas off) to chatter, to talk inconsequentially and continually, to offer only ‘hot air’.
2. [mid–late 19C; 2000s] (US campus) to deceive.
3. [late 19C–1910s] to boast.
4. [1940s] (US black) to tell, to inform.
[1960s] (US campus) to do badly on an examination.
see sense 1 above.
see talk one’s head off under talk v.
[late 19C–1910s] to ferret out information in a clandestine manner.
[2010s] to flatter, to deceive.