Beagle expert finally achieved a rare victory (6)
I believe the answer is:
darwin
'beagle expert' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'finally achieved a rare victory' is the wordplay.
'finally' says to take the final letters.
'rare' becomes 'r' (listed by Oxford Dictionary of Abbreviations).
'victory' becomes 'win' (a win is a victory).
The final letter of 'achieved' is 'd'.
'd'+'a'+'r'+'win'='DARWIN'
Can you help me to learn more?
(Other definitions for darwin that I've seen before include "Find the naturalist askey in ward 96)" , "Evolutionary pioneer" , "Aus. N. Territory capital" , "Author of On the Origin of Species, d.1882" , "He proposed the theory of evolution" .)