It is a rhetorical device like a metaphor, but the word creating the analogy must be closely related to its original meaning. For example, a thing that is not scary is made to represent a thing that is scary, as in “the pen is mightier than the sword.” The drama series, Game of Thrones, doubles down on metonymy with “game” referring to years of battles and intrigue, and “thrones” referring to the many seats of power across the fantasy world of Westeros. In Julius Caesar, Mark Antony says, “Friends, Romans, countrymen, lend me your ears.” Antony uses ears as a metonymy to ask the audience to listen to him.
It is a rhetorical device in which a part is made to represent the whole or vice versa, as in “all hands on deck,” which means all men on deck. When a knight puts his hands inside the hands of his lord, and the lord clasps the knight’s hands, this act of fealty shows that the knight is pledging loyalty to his lord. The hands of the lord are not all of him, but the hands represent him. Video games have numerous characters seeking or pledging loyalty.
In the 1962 Missal there is an oblation: O sovereign and true leader, O Christ, my king, I kneel before Thee here like a vassal in the old feudal times to take my oath of fealty. I place my joined hands within Thy wounded hands and promise Thee inviolable loyalty....