Diver involved in discovering Rebecca (5)
I believe the answer is:
grebe
'diver' is the definition.
(diving bird)
'involved in discovering rebecca' is the wordplay.
'involved in' says the answer is hidden in the clue.
'GREBE' is hidden in the letters of 'discovering rebecca'.
(Other definitions for grebe that I've seen before include "Freshwater diving bird" , "Crested water-bird" , "Swimmer" , "Small bird that builds floating nests" , "Diving water bird" .)