Be of the opinion it's deliberate (8)
I believe the answer is:
consider
'deliberate' is the definition.
(I know that deliberate can be written as consider)
'be of the opinion' is the wordplay.
I cannot quite understand how this works, but
'of' could be 'o' and 'o' is found within the answer.
'opinion' could be 'side' (side is a kind of opinion) and 'side' is located in the answer.
This explanation may well be incorrect...
'it's' is the link.
Can you help me to learn more?
(Other definitions for consider that I've seen before include "Suppose" , "Deliberate" , "Think about - judge" , "Look at someone or something thoughtfully" , "Think carefully about" .)