Green’s Dictionary of Slang

1. (orig. US) energy, ‘vim’.

1938

W. Winchell On Broadway 22 May [synd. col.] Loretta Young, George Brent and Mona Barrie never gave up, but they couldn’t put whammo into the dictionary-full they had to utter.

2. (US) something notable.

1970

‘Troy Conway’ Cunning Linguist (1973) 8: Three sets of whammos filled the eye, three incredibly sexy navels winked at me.

3. a muscular, toned male.

2018

Guardian 27 June 🌐 Men are hench, wammo or tonk.

4. the crux, the punch-line.

2021

J. Ellroy Widespread Panic 237: She went for the whammo, straight in.