In a Greek tragedy, irony and ________ are fused into one.

Greek Tragedy has several elements but most of all it uses dramatic irony in a tragedy.
Dramatic Irony can be defined as a dialogue or a situation that conveys one meaning to the character or characters on stage but coveys an opposite meaning to the audience. The use of dramatic irony often creates satirical situations and enhances the audience's pleasure.
Source: Oxford and ABC English Literature.