Answer: It is used as a negative and ironic word to describe Brutus.
Step-by-step explanation:
In Act III, Scene I of Julius Caesar, Caesar is brutally murdered by jealous conspirators.
In Act III, Scene II, Antony, a friend of Caesar's, argues that Brutus and his accomplices are 'honorable'. However, the constant repetition of this attribute creates the opposite effect.
Antony states that Brutus, an honorable man, said that Caesar was ambitious, and that Caesar has paid the price for this serious flaw. In this context, the word honorable is contrasted with the underlying accusations of murder, and thus carries the completely opposite meaning - that Brutus and his accomplices are murderers and are dishonorable.