Green’s Dictionary of Slang

(US) a blonde (woman).

1927		W. Winchell Your Broadway & Mine 29 Apr.. [synd. col.] Edna Leedom, the ondblay, went to an opening this week.
1929		A.T. Rogers ‘Casual Observer’ in Charlotte Obs. sect. 3 24 Feb. 8/8: She’s the one who did plenty of wise-cracking about the ondblay.