To swear on your friends and family or people you associate with often in gangs mostly used by GDs
Onfonem I'm finna sleep shorty ass .

Keep talking shit Imma beat yo ass onfonem.
by Kiddrevolution October 13, 2015
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A rudimentary type of 19th century telephone, the telephone relied on system of folks and their immediate friends to tension wires at a precise time in order to generate barometric frequencies that would route the users call to the appropriate destination by using a complex series of gears and pulleys.

Fun fact there are only 3 surviving onfonem operators left alive in the world!
“Hey try to keep it down in here, ally’s using the onfonem in the other room.”
by JSpinner November 3, 2023
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