Drake rueful for holding up announcement of discovery (6)
I believe the answer is:
eureka
'announcement of discovery' is the definition.
'eureka' can be an answer for 'discovery' (I have seen 'Brilliant discovery ' mean 'eureka' so perhaps 'discovery' could also mean 'eureka'). I'm not certain of the 'announcement of' bit.
'drake rueful for holding up' is the wordplay.
'holding' says the answer is hidden in the clue.
'up' is a reversal indicator (in down clue: letters go upwards).
'akerue' can be found hidden inside 'drake rueful for'.
'akerue' back-to-front is 'EUREKA'.
Can you help me to learn more?
(Other definitions for eureka that I've seen before include "Archimedes' cry of triumph as he ran naked through the streets of Syracuse?" , "Cry announcing a brilliant discovery" , "Cry of triumph (at a discovery)" , "Cry of joy on finding something" , "'I've made a discovery!'" .)