> 5 / to bring one’s hand toward one’s mouth without quite touching it Modesty. A gesture of eloquence employed by the great orators of antiquity.
AFAIK, this is the wrong explanation. The gesture is still in use today in Italy, and its meaning is different.
For example, the Middle Eastern hand gesture for "stop" is totally different than American hand signals. The confusion probably caused at least a few of the hundreds of Iraqi civilians shot at traffic checkpoints by US soldiers. https://savageminds.org/2008/09/28/how-not-to-signal-stop/