Beginning to see bad actor's insincere (4)
I believe the answer is:
sham
'insincere' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I can't see?
'beginning to see bad actor's' is the wordplay.
'beginning to' indicates taking the first letters.
'bad actor' becomes 'ham' (a ham is someone who overacts).
The first letter of 'see' is 's'.
's'+'ham'='SHAM'
Can you help me to learn more?
(Other definitions for sham that I've seen before include "Bogus hams" , "'Fake, pseudo (4)'" , "Feign" , "Mash, being counterfeit" , "Cheap falseness" .)