The Prince threatened Lords Capulet and Montague that their lives would be forfeit if another feud occurred between their families.  In this context, forfeit means

The Nurse is eager to warrant the truth of nearly every story she tells. In this context, warrant means

Although Rosaline is chaste, she still flirts with Romeo. In this context, chaste means 

Romeo feels that Rosaline's eyes are exquisite. In this context, exquisite means 

Tybalt, Lady Capulet's nephew, sees himself as Romeo's chief adversary. In this context, adversary means

Not knowing the exact cause of the feud between the Capulets and Montagues augments the pettiness of the revenge. 

In this context, augments means

When Romeo and his friends crash the Capulets' party, Tybalt feels he has a grievance against them. In this context, grievance means 

Romeo told Juliet that her kiss would purge any sin from his lips. In this context, purge means 

The Prince sees the hatred between the Capulets and Montagues as pernicious. In this context, pernicious means

Tybalt feels that the banquet is an occasion for great solemnity. In this context, solemnity means