Solitary clue is very nearly tricky (9)
I believe the answer is:
reclusive
'solitary' is the definition.
(thesaurus)
'clue is very nearly tricky' is the wordplay.
'nearly' means to remove the last letter.
'tricky' is an anagram indicator.
'clue'+'is'+'very'='clueisvery'
'clueisvery' with its last letter taken away is 'clueisver'.
'clueisver' with letters rearranged gives 'RECLUSIVE'.
(Other definitions for reclusive that I've seen before include "retiring" , "Hermit-like" , "Solitary" .)