Conservative cracking nuts was Etonian genius (5,6)
I believe the answer is:
isaac newton
'genius' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'conservative cracking nuts was etonian' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'cracking' means one lot of letters goes inside another (inserted letters go into a gap or crack).
'nuts' indicates an anagram (nuts can mean crazy).
'was'+'etonian'='wasetonian'
'wasetonian' with letters rearranged gives 'isaanewton'.
'c' put within 'isaanewton' is 'ISAAC NEWTON'.
Can you help me to learn more?
(Other definitions for isaac newton that I've seen before include "English mathematician and physicist" , "Lawmaker" , "Principia author" , "noted scientist" , "Seventeenth to eighteenth century English physicist/mathematician" .)