A correspondent in Notes and Queries (March 5th, 1892) suggests as the fons et orīgo of this word the Italian Uomo bugiardo, a lying man.
⁂ To hum used to signify “to applaud,” “to pretend admiration,” hence “to flatter,” “to cajole for an end,” “to deceive.”
“He threatened, but behold! ‘twas all a hum.”
“‘Gentlemen, this humming [expression of applause] is not at all becoming the gravity of this court.”—State Trials (1660).