“Well, in that hit you miss: she'll not be hit, With Cupid's arrow; she hath Dian's wit” is an example of an allusion.
An allusion is an expression designed to call something to mind without mentioning it explicitly. In this scene Romeo is complaining that Rosaline does not love him. Romeo said that she is too smart to fall in love with him. He compares her to Dian who was a sworn virgin.
