The title of the play—Much Ado About Nothing—represents a pun. In Elizabethan times, the word “nothing” would have been pronounced as “noting,” which has the additional meaning of “eavesdropping.” This pun thus prepares the audience for moments such as this exchange between Leonato and Antonio. These characters are making much of “noting”—Antonio’s eavesdropping—as well as “nothing,” for it is all a misunderstanding.

“Peradventure” is an archaic form of the word “perhaps,” meaning that Leonato is somewhat suspicious about the truth of the rumor he has just heard. However, Leonato asks Antonio to make sure that Hero is “prepared for an answer” since he wants to warn her of Claudio’s potential proposal. Shakespeare here introduces the theme of the performative nature of love. Hero is essentially being instructed on how to behave in this situation before it happens (like an actress.) At the same time, Claudio and Don Pedro are staging their own play of sorts to win Claudio Hero’s affection.

Antonio is relating information that he has heard through his “sharp” trusted servant, but Leonato is not entirely convinced of its veracity. Here, Shakespeare introduces the theme of perception, miscommunication, and misconception. Throughout the play, pay attention to the ways in which characters’ perceptions of reality are determined by misunderstandings, rumors, and deceit.

In other words, be very careful during this busy time.

This bit of dialogue opens the theme of misunderstanding that begins innocently (as in this example) but becomes much more serious later on.

In modern terms, this would be Leonato's nephew.  In Elizabethan times, the word cousin is loosely used to mean any relatively close relative.