I muscle out crook, being thorough (10)
I believe the answer is:
meticulous
'thorough' is the definition.
(thesaurus)
'i muscle out crook' is the wordplay.
'crook' indicates an anagram (a crooked or broken form of the letters).
'i'+'muscle'+'out'='imuscleout'
'imuscleout' is an anagram of 'METICULOUS'.
'being' acts as a link.
(Other definitions for meticulous that I've seen before include "of great precision" , "Extremely careful" .)