defy
disregard or disobey
labour
refers to the pain of waiting for the beloved to undress herself
foe
Donne's love is the 'foe' here as the beloved is still not ready to give herself completely to the poet
girdle
her lower garments
coronet
a small and simple crown, especially as worn by lesser royalty
discovering thee
exploring the beauty of beloved's body
A heaven like Mahomet's paradise
An example of metaphysical conceit. In Muslim dogma, it is believed that virgins live in heaven and he is comparing his beloved to those virgins.
licence my roving hands
give me permission to touch you allover
Atlanta's ball
Atlanta is taken from Greek mythology. It is said that she did not want to marry but agreed on marrying the man who could defeat her in a footrace, when her father was upset with her decision. In the race, a man called Hippomenes threw golden apples in order to distract Atalanta. He actually won the race and married her.
thy midwife show
Just like a woman does not hesitate in showing her body to a midwife, the beloved should also present herself to Donne wholeheartedly.
no penance due to innocence
The idea of virginity and sexuality is not related to innocence and therefore there is no scope of penance at all.