Bob turns out to be obstinate (8)
I believe the answer is:
stubborn
'be obstinate' is the definition.
(synonyms)
'bob turns out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'bob'+'turns'='bobturns'
'bobturns' anagrammed gives 'STUBBORN'.
'to' is the link.
(Other definitions for stubborn that I've seen before include "Obstinate, unwilling to yield" , "Unwilling to yield or grant a point" , "Obdurate and unyielding (8)" , "Rigid" , "Determined" .)