1. brand: torch.
2. maid of Dian's: votaress of Diana, goddess of chastity. advantage: opportunity.
3. steep: immerse.
6. dateless: endless; eternal. still: always.
7. grew: became. seething bath: spring of hot, bubbling, medicinal waters. prove: evince as proof.
9. But at my mistress' eye Love's brand new fired: Love has kindled his torch from the mistress' eyes.
10. for trial: to test it.
11. withal: from that.
12. hied: hastened. distemper'd: ill.