Nurse not the first to swallow unknown aphrodisiac (6)
I believe the answer is:
oyster
'aphrodisiac' is the definition.
(oysters are supposedly aphrodisiacs)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for oyster that I've seen before include "The world of Shakespeare" , "Succulent bivalve, may bear a pearl" , "Edible shellfish" , "Pearl-bearing sea creature" , "person unwilling to communicate" .)