Inscrutable setter's met with a lot of criticism (6)
I believe the answer is:
mystic
'inscrutable' is the definition.
(thesaurus)
'setter's met with a lot of criticism' is the wordplay.
'setter's' becomes 'my' (belonging to the crossword setter).
'met with' says to put letters next to each other.
'a lot of' means to remove the last letter (a lot of but not all of the word).
'criticism' becomes 'stick' (giving someone stick is criticising them).
'stick' with its last letter taken off is 'stic'.
'my'+'stic'='MYSTIC'
(Other definitions for mystic that I've seen before include "intensely spiritual" , "Allegorical; sacredly obscure" , "One attaining high levels of spirituality" , "Seer" , "Esoteric" .)