Tense and certainly not flawless (9)
I believe the answer is:
imperfect
'tense' is the definition.
(the imperfect tense is a grammatical tense)
'certainly not flawless' is the wordplay.
'certainly not' becomes 'im' (I am not sure about this - if you are sure you should believe this answer much more).
'flawless' becomes 'perfect' (similar in meaning).
'im'+'perfect'='IMPERFECT'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for imperfect that I've seen before include "Deficient" , "seconds" , "Flawed, defective" , "being immature" , "Faulty; tense" .)