Consider an unconvincing ending for a book (5)
I believe the answer is:
think
'consider' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for think that I've seen before include "Cogitate; deem" , "Believe" , "Imagine" , "Use one's mind" , "Ponder" .)