Undistinguished character (7)
I believe the answer is:
someone
'character' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for someone that I've seen before include "A person (maybe of importance)" , "Unspecified person" , "An unknown person" , "individual" , "big cheese" .)