Referring back to subject of Felix, ever cryptic! (9)
I believe the answer is:
reflexive
'referring back to subject' is the definition.
'felix ever cryptic' is the wordplay.
'cryptic' is an anagram indicator.
'felix'+'ever'='felixever'
'felixever' is an anagram of 'REFLEXIVE'.
'of' is the link.
(Other definitions for reflexive that I've seen before include "Kind of pronoun like myself, himself etc" , "(Of an action) done without conscious thought" , "Of word, referring back to subject of verb" , "(Of an action) performed unconsciously" .)