Detective close to body that's not in good condition (5)
I believe the answer is:
dicky
'not in good condition' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'detective close to body' is the wordplay.
'detective' becomes 'dick' (informal term for a detective).
'close to' indicates one should take the final letters (the 'close' to the word).
The final letter of 'body' is 'y'.
'dick'+'y'='DICKY'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for dicky that I've seen before include "Rotten" , "Unreliable" , "likely to fail" , "tie" , "In precarious health - bird?" .)