Naughty boy keeping eagle's last brood in an unhealthy condition (7)
I believe the answer is:
obesity
'an unhealthy condition' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'naughty boy keeping eagle's last brood' is the wordplay.
'naughty' is an anagram indicator.
'keeping' means one lot of letters goes inside another.
'last' indicates one should take the final letters.
'brood' becomes 'sit' (I've seen this before).
The last letter of 'eagle' is 'e'.
'boy' anagrammed gives 'oby'.
'e'+'sit'='esit'
'oby' enclosing 'esit' is 'OBESITY'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for obesity that I've seen before include "Condition of excessive fatness" , "State of unhealthy fatness" , "Fatness to great excess" , "Corpulence" , "Gross fatness" .)