Fraudulent thesis Don concocted (9)
I believe the answer is:
dishonest
'fraudulent' is the definition.
(similar in meaning)
'thesis don concocted' is the wordplay.
'concocted' indicates anagramming the letters.
'thesis'+'don'='thesisdon'
'thesisdon' is an anagram of 'DISHONEST'.
(Other definitions for dishonest that I've seen before include "Not true!" , "Fraudulent" , "Untrustworthy" , "Corrupt" , "Not straightforward" .)