Socrates use of the word "Herculean" in this excerpt from the apology is an example of what literally device?

The word "Herculean" is an example of allusion. Allusion is a literary device which is an indirect reference to a person, thing or idea related to some important incident, literary work, or historical event.

In this particular context, the word "Herculean" makes reference to the mythological hero Hercules. This word is used as an adjective that describe a situation which requires a great ability and strength.