backbeat, n. — Green’s Dictionary of Slang

backbeat n.

[jazz use backbeat, a secondary beat that underlies the main theme]

(US black)

one’s heartbeat.

1994

backbeat of the trey thirty (n.) [trey n.]

(US black/Harlem) the third day of the month.

1944

D. Burley Orig. Hbk of Harlem Jive 15: I dug a skull a deuce of haircuts on the backbeat of the trey thirty putting down a spiel on a heavy hen.

on the backbeat (also on the way back)

(US black/Harlem) of time, in the past, ago; before.

1943		D. Burley N.Y. Amsterdam Star-News 13 Mar. 13: [M]y snatch spread flew me a slight kite on the early brights , a deuce of haircuts on the way back.
1944		D. Burley Orig. Hbk of Harlem Jive 12: Ole man, it’s about a tray of haircuts on the backbeat when I nixes my pad.